Re: [FFmpeg-devel] [PATCH] lavc: reset codec on receiving packet after EOF in compat_decode
On Sat, Dec 09, 2017 at 09:46:53PM +0100, Marton Balint wrote:
>
>
> On Mon, 27 Nov 2017, Michael Niedermayer wrote:
>
> >On Sun, Nov 26, 2017 at 12:09:35PM -0300, James Almer wrote:
> >>On 11/21/2017 6:48 PM, Marton Balint wrote:
> >>>
> >>>
> >>>On Thu, 9 Nov 2017, James Cowgill wrote:
> >>>
> Hi,
>
> On 09/11/17 14:02, Hendrik Leppkes wrote:
> >On Thu, Nov 9, 2017 at 1:21 PM, James Cowgill
> >wrote:
> >>In commit 061a0c14bb57 ("decode: restructure the core decoding
> >>code"), the
> >>deprecated avcodec_decode_* APIs were reworked so that they called
> >>into the
> >>new avcodec_send_packet / avcodec_receive_frame API. This had the
> >>side effect
> >>of prohibiting sending new packets containing data after a drain
> >>packet, but in previous versions of FFmpeg this "worked" and some
> >>applications relied on it.
> >>
> >>To restore some compatibility, reset the codec if we receive a new
> >>non-drain
> >>packet using the old API after draining has completed. While this does
> >>not give the same behaviour as the old API did, in the majority of
> >>cases
> >>it works and it does not require changes to any other part of the
> >>decoding
> >>code.
> >>
> >>Fixes ticket #6775
> >>Signed-off-by: James Cowgill
> >>---
> >> libavcodec/decode.c | 5 +
> >> 1 file changed, 5 insertions(+)
> >>
> >>diff --git a/libavcodec/decode.c b/libavcodec/decode.c
> >>index 86fe5aef52..2f1932fa85 100644
> >>--- a/libavcodec/decode.c
> >>+++ b/libavcodec/decode.c
> >>@@ -726,6 +726,11 @@ static int compat_decode(AVCodecContext *avctx,
> >>AVFrame *frame,
> >>
> >> av_assert0(avci->compat_decode_consumed == 0);
> >>
> >>+ if (avci->draining_done && pkt && pkt->size != 0) {
> >>+ av_log(avctx, AV_LOG_WARNING, "Got unexpected packet after
> >>EOF\n");
> >>+ avcodec_flush_buffers(avctx);
> >>+ }
> >>+
> >
> >I don't think this is a good idea. Draining and not flushing
> >afterwards is a bug in the calling code, and even before recent
> >changes it would result in inconsistent behavior and even crashes
> >(with select decoders).
>
> I am fully aware that this will only trigger if the calling code is
> buggy. I am trying to avoid silent breakage of those applications doing
> this when upgrading to ffmpeg 3.4.
>
> I was looking at the documentation of avcodec_decode_* recently because
> of this and I had some trouble deciding if using the API this way was
> incorrect. I expect the downstreams affected thought that what they were
> doing was fine and then got angry when ffmpeg suddenly "broke" their
> code. This patch at least allows some sort of "transitional period"
> until downstreams update.
> >>>
> >>>I think the intent was to flush the codec by passing the NULL packets to
> >>>it, so it makes a lot of sense to actually do that. Especially since by
> >>>implicitly doing a flush, we can avoid the undefined behaviour/crashes
> >>>on the codec side.
> >>>
> >>>Also this is only compatibility code, which probably will be removed at
> >>>the next bump, I see no harm in making it as compatible as realistically
> >>>possible.
> >>
> >>The old decode API is not scheduled for removal right now probably
> >>because 99% of decoders need to be ported.
> >>This compat code was written so the old API becomes a wrapper for the
> >>new rather than the other way around, as it was up to 3.3. Supposedly a
> >>good portion of the versatility of the new API would be handicapped
> >>otherwise.
> >>
> >
> >>Personally, I think this should be left as is. It is a good incentive
> >>for downstream to migrate to the new API, as they technically were
> >>misusing the old API to begin with.
> >
> >providing compatibility support for an old API that does not actually
> >work with how applications used the old API is something a tad bit
> >bizzare
> >
> >We want to minimize the work everyone has to do.
> >The more time people have, the more they can spend on improving free
> >software.
> >
> >If the old API is going to be removed, any work people have to do
> >to hunt and track implementation changes in our old API the more
> >they have wasted time.
> >If you want people to spend their time on the new API, then you
> >should not introduce issues in the old API that they need to
> >workaround
> >They that way just lost time (debug, fix, test) they could have spend
> >on the new API or on anything else
> >
>
> Applied and backported.
Thanks alot !
[...]
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Re: [FFmpeg-devel] [PATCH] lavc: reset codec on receiving packet after EOF in compat_decode
On Mon, 27 Nov 2017, Michael Niedermayer wrote:
On Sun, Nov 26, 2017 at 12:09:35PM -0300, James Almer wrote:
On 11/21/2017 6:48 PM, Marton Balint wrote:
On Thu, 9 Nov 2017, James Cowgill wrote:
Hi,
On 09/11/17 14:02, Hendrik Leppkes wrote:
On Thu, Nov 9, 2017 at 1:21 PM, James Cowgill
wrote:
In commit 061a0c14bb57 ("decode: restructure the core decoding
code"), the
deprecated avcodec_decode_* APIs were reworked so that they called
into the
new avcodec_send_packet / avcodec_receive_frame API. This had the
side effect
of prohibiting sending new packets containing data after a drain
packet, but in previous versions of FFmpeg this "worked" and some
applications relied on it.
To restore some compatibility, reset the codec if we receive a new
non-drain
packet using the old API after draining has completed. While this does
not give the same behaviour as the old API did, in the majority of
cases
it works and it does not require changes to any other part of the
decoding
code.
Fixes ticket #6775
Signed-off-by: James Cowgill
---
libavcodec/decode.c | 5 +
1 file changed, 5 insertions(+)
diff --git a/libavcodec/decode.c b/libavcodec/decode.c
index 86fe5aef52..2f1932fa85 100644
--- a/libavcodec/decode.c
+++ b/libavcodec/decode.c
@@ -726,6 +726,11 @@ static int compat_decode(AVCodecContext *avctx,
AVFrame *frame,
av_assert0(avci->compat_decode_consumed == 0);
+ if (avci->draining_done && pkt && pkt->size != 0) {
+ av_log(avctx, AV_LOG_WARNING, "Got unexpected packet after
EOF\n");
+ avcodec_flush_buffers(avctx);
+ }
+
I don't think this is a good idea. Draining and not flushing
afterwards is a bug in the calling code, and even before recent
changes it would result in inconsistent behavior and even crashes
(with select decoders).
I am fully aware that this will only trigger if the calling code is
buggy. I am trying to avoid silent breakage of those applications doing
this when upgrading to ffmpeg 3.4.
I was looking at the documentation of avcodec_decode_* recently because
of this and I had some trouble deciding if using the API this way was
incorrect. I expect the downstreams affected thought that what they were
doing was fine and then got angry when ffmpeg suddenly "broke" their
code. This patch at least allows some sort of "transitional period"
until downstreams update.
I think the intent was to flush the codec by passing the NULL packets to
it, so it makes a lot of sense to actually do that. Especially since by
implicitly doing a flush, we can avoid the undefined behaviour/crashes
on the codec side.
Also this is only compatibility code, which probably will be removed at
the next bump, I see no harm in making it as compatible as realistically
possible.
The old decode API is not scheduled for removal right now probably
because 99% of decoders need to be ported.
This compat code was written so the old API becomes a wrapper for the
new rather than the other way around, as it was up to 3.3. Supposedly a
good portion of the versatility of the new API would be handicapped
otherwise.
Personally, I think this should be left as is. It is a good incentive
for downstream to migrate to the new API, as they technically were
misusing the old API to begin with.
providing compatibility support for an old API that does not actually
work with how applications used the old API is something a tad bit
bizzare
We want to minimize the work everyone has to do.
The more time people have, the more they can spend on improving free
software.
If the old API is going to be removed, any work people have to do
to hunt and track implementation changes in our old API the more
they have wasted time.
If you want people to spend their time on the new API, then you
should not introduce issues in the old API that they need to
workaround
They that way just lost time (debug, fix, test) they could have spend
on the new API or on anything else
Applied and backported.
Regards,
Marton
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Re: [FFmpeg-devel] [PATCH] lavc: reset codec on receiving packet after EOF in compat_decode
On Sun, Nov 26, 2017 at 12:09:35PM -0300, James Almer wrote:
> On 11/21/2017 6:48 PM, Marton Balint wrote:
> >
> >
> > On Thu, 9 Nov 2017, James Cowgill wrote:
> >
> >> Hi,
> >>
> >> On 09/11/17 14:02, Hendrik Leppkes wrote:
> >>> On Thu, Nov 9, 2017 at 1:21 PM, James Cowgill
> >>> wrote:
> In commit 061a0c14bb57 ("decode: restructure the core decoding
> code"), the
> deprecated avcodec_decode_* APIs were reworked so that they called
> into the
> new avcodec_send_packet / avcodec_receive_frame API. This had the
> side effect
> of prohibiting sending new packets containing data after a drain
> packet, but in previous versions of FFmpeg this "worked" and some
> applications relied on it.
>
> To restore some compatibility, reset the codec if we receive a new
> non-drain
> packet using the old API after draining has completed. While this does
> not give the same behaviour as the old API did, in the majority of
> cases
> it works and it does not require changes to any other part of the
> decoding
> code.
>
> Fixes ticket #6775
> Signed-off-by: James Cowgill
> ---
> libavcodec/decode.c | 5 +
> 1 file changed, 5 insertions(+)
>
> diff --git a/libavcodec/decode.c b/libavcodec/decode.c
> index 86fe5aef52..2f1932fa85 100644
> --- a/libavcodec/decode.c
> +++ b/libavcodec/decode.c
> @@ -726,6 +726,11 @@ static int compat_decode(AVCodecContext *avctx,
> AVFrame *frame,
>
> av_assert0(avci->compat_decode_consumed == 0);
>
> + if (avci->draining_done && pkt && pkt->size != 0) {
> + av_log(avctx, AV_LOG_WARNING, "Got unexpected packet after
> EOF\n");
> + avcodec_flush_buffers(avctx);
> + }
> +
> >>>
> >>> I don't think this is a good idea. Draining and not flushing
> >>> afterwards is a bug in the calling code, and even before recent
> >>> changes it would result in inconsistent behavior and even crashes
> >>> (with select decoders).
> >>
> >> I am fully aware that this will only trigger if the calling code is
> >> buggy. I am trying to avoid silent breakage of those applications doing
> >> this when upgrading to ffmpeg 3.4.
> >>
> >> I was looking at the documentation of avcodec_decode_* recently because
> >> of this and I had some trouble deciding if using the API this way was
> >> incorrect. I expect the downstreams affected thought that what they were
> >> doing was fine and then got angry when ffmpeg suddenly "broke" their
> >> code. This patch at least allows some sort of "transitional period"
> >> until downstreams update.
> >
> > I think the intent was to flush the codec by passing the NULL packets to
> > it, so it makes a lot of sense to actually do that. Especially since by
> > implicitly doing a flush, we can avoid the undefined behaviour/crashes
> > on the codec side.
> >
> > Also this is only compatibility code, which probably will be removed at
> > the next bump, I see no harm in making it as compatible as realistically
> > possible.
>
> The old decode API is not scheduled for removal right now probably
> because 99% of decoders need to be ported.
> This compat code was written so the old API becomes a wrapper for the
> new rather than the other way around, as it was up to 3.3. Supposedly a
> good portion of the versatility of the new API would be handicapped
> otherwise.
>
> Personally, I think this should be left as is. It is a good incentive
> for downstream to migrate to the new API, as they technically were
> misusing the old API to begin with.
providing compatibility support for an old API that does not actually
work with how applications used the old API is something a tad bit
bizzare
We want to minimize the work everyone has to do.
The more time people have, the more they can spend on improving free
software.
If the old API is going to be removed, any work people have to do
to hunt and track implementation changes in our old API the more
they have wasted time.
If you want people to spend their time on the new API, then you
should not introduce issues in the old API that they need to
workaround
They that way just lost time (debug, fix, test) they could have spend
on the new API or on anything else
> Between fixing their old API usage and migrating, the choice should be
> obvious.
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> http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
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Re: [FFmpeg-devel] [PATCH] lavc: reset codec on receiving packet after EOF in compat_decode
Marton Balint (2017-11-26): > Okay, I am exagarating a bit, but unconditionally returning AVERROR(ENOSYS) > would be an even better incentive, no? :) For invalid uses of the API that can be easily avoided by the application (like not explicitly passing NULL to a function), a hard crash is even better. Regards, -- Nicolas George signature.asc Description: Digital signature ___ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
Re: [FFmpeg-devel] [PATCH] lavc: reset codec on receiving packet after EOF in compat_decode
On Sun, 26 Nov 2017, James Almer wrote: On 11/26/2017 12:19 PM, Nicolas George wrote: James Almer (2017-11-26): The old decode API is not scheduled for removal right now probably because 99% of decoders need to be ported. I think this statement contains some confusion that is harmful to the discussion. There are two interfaces worth considering in this discussion: the application -> library interface, i.e. the avcodec_decode_*dio() functions, and the framework -> decoder interface, i.e. the decode / receive_frame / ... callbacks. When you are stating "because 99% of decoders need to be ported", you are referring to the framework-decoder interface. On the other hand, the misuse of the API that is at the origin of this thread is related to the application-library interface. Yes, my bad. Got the public API and the internal callbacks mixed. So ignore that part. Guess then that the functions did not get a removal schedule because they are still too ubiquitous downstream. My second paragraph stands, in any case. I consider this a good chance to get downstreams to migrate. Okay, I am exagarating a bit, but unconditionally returning AVERROR(ENOSYS) would be an even better incentive, no? :) We can blame API usage (we should rather blame unclear documentation), but no matter how we put it, with the change, we broke the user experience of two major projects. If fixing it (at least partially) is so easy, I still don't see why we should not do that. People who still oppose this change, please respond. Thanks, Marton ___ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
Re: [FFmpeg-devel] [PATCH] lavc: reset codec on receiving packet after EOF in compat_decode
On 11/26/2017 12:19 PM, Nicolas George wrote: > James Almer (2017-11-26): >> The old decode API is not scheduled for removal right now probably >> because 99% of decoders need to be ported. > > I think this statement contains some confusion that is harmful to the > discussion. > > There are two interfaces worth considering in this discussion: the > application -> library interface, i.e. the avcodec_decode_*dio() > functions, and the framework -> decoder interface, i.e. the decode / > receive_frame / ... callbacks. > > When you are stating "because 99% of decoders need to be ported", you > are referring to the framework-decoder interface. On the other hand, the > misuse of the API that is at the origin of this thread is related to the > application-library interface. Yes, my bad. Got the public API and the internal callbacks mixed. So ignore that part. Guess then that the functions did not get a removal schedule because they are still too ubiquitous downstream. My second paragraph stands, in any case. I consider this a good chance to get downstreams to migrate. > > We could deprecate avcodec_decode_*dio() right now even though the > decoders are not all ported. They are already deprecated. I assume you meant remove. > > Regards, > > > > ___ > ffmpeg-devel mailing list > ffmpeg-devel@ffmpeg.org > http://ffmpeg.org/mailman/listinfo/ffmpeg-devel > ___ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
Re: [FFmpeg-devel] [PATCH] lavc: reset codec on receiving packet after EOF in compat_decode
James Almer (2017-11-26): > The old decode API is not scheduled for removal right now probably > because 99% of decoders need to be ported. I think this statement contains some confusion that is harmful to the discussion. There are two interfaces worth considering in this discussion: the application -> library interface, i.e. the avcodec_decode_*dio() functions, and the framework -> decoder interface, i.e. the decode / receive_frame / ... callbacks. When you are stating "because 99% of decoders need to be ported", you are referring to the framework-decoder interface. On the other hand, the misuse of the API that is at the origin of this thread is related to the application-library interface. We could deprecate avcodec_decode_*dio() right now even though the decoders are not all ported. Regards, -- Nicolas George signature.asc Description: Digital signature ___ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
Re: [FFmpeg-devel] [PATCH] lavc: reset codec on receiving packet after EOF in compat_decode
On 11/21/2017 6:48 PM, Marton Balint wrote:
>
>
> On Thu, 9 Nov 2017, James Cowgill wrote:
>
>> Hi,
>>
>> On 09/11/17 14:02, Hendrik Leppkes wrote:
>>> On Thu, Nov 9, 2017 at 1:21 PM, James Cowgill
>>> wrote:
In commit 061a0c14bb57 ("decode: restructure the core decoding
code"), the
deprecated avcodec_decode_* APIs were reworked so that they called
into the
new avcodec_send_packet / avcodec_receive_frame API. This had the
side effect
of prohibiting sending new packets containing data after a drain
packet, but in previous versions of FFmpeg this "worked" and some
applications relied on it.
To restore some compatibility, reset the codec if we receive a new
non-drain
packet using the old API after draining has completed. While this does
not give the same behaviour as the old API did, in the majority of
cases
it works and it does not require changes to any other part of the
decoding
code.
Fixes ticket #6775
Signed-off-by: James Cowgill
---
libavcodec/decode.c | 5 +
1 file changed, 5 insertions(+)
diff --git a/libavcodec/decode.c b/libavcodec/decode.c
index 86fe5aef52..2f1932fa85 100644
--- a/libavcodec/decode.c
+++ b/libavcodec/decode.c
@@ -726,6 +726,11 @@ static int compat_decode(AVCodecContext *avctx,
AVFrame *frame,
av_assert0(avci->compat_decode_consumed == 0);
+ if (avci->draining_done && pkt && pkt->size != 0) {
+ av_log(avctx, AV_LOG_WARNING, "Got unexpected packet after
EOF\n");
+ avcodec_flush_buffers(avctx);
+ }
+
>>>
>>> I don't think this is a good idea. Draining and not flushing
>>> afterwards is a bug in the calling code, and even before recent
>>> changes it would result in inconsistent behavior and even crashes
>>> (with select decoders).
>>
>> I am fully aware that this will only trigger if the calling code is
>> buggy. I am trying to avoid silent breakage of those applications doing
>> this when upgrading to ffmpeg 3.4.
>>
>> I was looking at the documentation of avcodec_decode_* recently because
>> of this and I had some trouble deciding if using the API this way was
>> incorrect. I expect the downstreams affected thought that what they were
>> doing was fine and then got angry when ffmpeg suddenly "broke" their
>> code. This patch at least allows some sort of "transitional period"
>> until downstreams update.
>
> I think the intent was to flush the codec by passing the NULL packets to
> it, so it makes a lot of sense to actually do that. Especially since by
> implicitly doing a flush, we can avoid the undefined behaviour/crashes
> on the codec side.
>
> Also this is only compatibility code, which probably will be removed at
> the next bump, I see no harm in making it as compatible as realistically
> possible.
The old decode API is not scheduled for removal right now probably
because 99% of decoders need to be ported.
This compat code was written so the old API becomes a wrapper for the
new rather than the other way around, as it was up to 3.3. Supposedly a
good portion of the versatility of the new API would be handicapped
otherwise.
Personally, I think this should be left as is. It is a good incentive
for downstream to migrate to the new API, as they technically were
misusing the old API to begin with.
Between fixing their old API usage and migrating, the choice should be
obvious.
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Re: [FFmpeg-devel] [PATCH] lavc: reset codec on receiving packet after EOF in compat_decode
On Tue, Nov 21, 2017 at 10:48:19PM +0100, Marton Balint wrote:
>
>
> On Thu, 9 Nov 2017, James Cowgill wrote:
>
> >Hi,
> >
> >On 09/11/17 14:02, Hendrik Leppkes wrote:
> >>On Thu, Nov 9, 2017 at 1:21 PM, James Cowgill wrote:
> >>>In commit 061a0c14bb57 ("decode: restructure the core decoding code"), the
> >>>deprecated avcodec_decode_* APIs were reworked so that they called into the
> >>>new avcodec_send_packet / avcodec_receive_frame API. This had the side
> >>>effect
> >>>of prohibiting sending new packets containing data after a drain
> >>>packet, but in previous versions of FFmpeg this "worked" and some
> >>>applications relied on it.
> >>>
> >>>To restore some compatibility, reset the codec if we receive a new
> >>>non-drain
> >>>packet using the old API after draining has completed. While this does
> >>>not give the same behaviour as the old API did, in the majority of cases
> >>>it works and it does not require changes to any other part of the decoding
> >>>code.
> >>>
> >>>Fixes ticket #6775
> >>>Signed-off-by: James Cowgill
> >>>---
> >>> libavcodec/decode.c | 5 +
> >>> 1 file changed, 5 insertions(+)
> >>>
> >>>diff --git a/libavcodec/decode.c b/libavcodec/decode.c
> >>>index 86fe5aef52..2f1932fa85 100644
> >>>--- a/libavcodec/decode.c
> >>>+++ b/libavcodec/decode.c
> >>>@@ -726,6 +726,11 @@ static int compat_decode(AVCodecContext *avctx,
> >>>AVFrame *frame,
> >>>
> >>> av_assert0(avci->compat_decode_consumed == 0);
> >>>
> >>>+if (avci->draining_done && pkt && pkt->size != 0) {
> >>>+av_log(avctx, AV_LOG_WARNING, "Got unexpected packet after
> >>>EOF\n");
> >>>+avcodec_flush_buffers(avctx);
> >>>+}
> >>>+
> >>
> >>I don't think this is a good idea. Draining and not flushing
> >>afterwards is a bug in the calling code, and even before recent
> >>changes it would result in inconsistent behavior and even crashes
> >>(with select decoders).
> >
> >I am fully aware that this will only trigger if the calling code is
> >buggy. I am trying to avoid silent breakage of those applications doing
> >this when upgrading to ffmpeg 3.4.
> >
> >I was looking at the documentation of avcodec_decode_* recently because
> >of this and I had some trouble deciding if using the API this way was
> >incorrect. I expect the downstreams affected thought that what they were
> >doing was fine and then got angry when ffmpeg suddenly "broke" their
> >code. This patch at least allows some sort of "transitional period"
> >until downstreams update.
>
> I think the intent was to flush the codec by passing the NULL
> packets to it, so it makes a lot of sense to actually do that.
> Especially since by implicitly doing a flush, we can avoid the
> undefined behaviour/crashes on the codec side.
>
> Also this is only compatibility code, which probably will be removed
> at the next bump, I see no harm in making it as compatible as
> realistically possible.
i agree and i would appreciate if this gets resolved one way or another
so i can make the release
Thanks
[...]
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Re: [FFmpeg-devel] [PATCH] lavc: reset codec on receiving packet after EOF in compat_decode
On Thu, 9 Nov 2017, James Cowgill wrote:
Hi,
On 09/11/17 14:02, Hendrik Leppkes wrote:
On Thu, Nov 9, 2017 at 1:21 PM, James Cowgill wrote:
In commit 061a0c14bb57 ("decode: restructure the core decoding code"), the
deprecated avcodec_decode_* APIs were reworked so that they called into the
new avcodec_send_packet / avcodec_receive_frame API. This had the side effect
of prohibiting sending new packets containing data after a drain
packet, but in previous versions of FFmpeg this "worked" and some
applications relied on it.
To restore some compatibility, reset the codec if we receive a new non-drain
packet using the old API after draining has completed. While this does
not give the same behaviour as the old API did, in the majority of cases
it works and it does not require changes to any other part of the decoding
code.
Fixes ticket #6775
Signed-off-by: James Cowgill
---
libavcodec/decode.c | 5 +
1 file changed, 5 insertions(+)
diff --git a/libavcodec/decode.c b/libavcodec/decode.c
index 86fe5aef52..2f1932fa85 100644
--- a/libavcodec/decode.c
+++ b/libavcodec/decode.c
@@ -726,6 +726,11 @@ static int compat_decode(AVCodecContext *avctx, AVFrame
*frame,
av_assert0(avci->compat_decode_consumed == 0);
+if (avci->draining_done && pkt && pkt->size != 0) {
+av_log(avctx, AV_LOG_WARNING, "Got unexpected packet after EOF\n");
+avcodec_flush_buffers(avctx);
+}
+
I don't think this is a good idea. Draining and not flushing
afterwards is a bug in the calling code, and even before recent
changes it would result in inconsistent behavior and even crashes
(with select decoders).
I am fully aware that this will only trigger if the calling code is
buggy. I am trying to avoid silent breakage of those applications doing
this when upgrading to ffmpeg 3.4.
I was looking at the documentation of avcodec_decode_* recently because
of this and I had some trouble deciding if using the API this way was
incorrect. I expect the downstreams affected thought that what they were
doing was fine and then got angry when ffmpeg suddenly "broke" their
code. This patch at least allows some sort of "transitional period"
until downstreams update.
I think the intent was to flush the codec by passing the NULL packets to
it, so it makes a lot of sense to actually do that. Especially since by
implicitly doing a flush, we can avoid the undefined behaviour/crashes on
the codec side.
Also this is only compatibility code, which probably will be removed at
the next bump, I see no harm in making it as compatible as realistically
possible.
Regards,
Marton
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Re: [FFmpeg-devel] [PATCH] lavc: reset codec on receiving packet after EOF in compat_decode
Hi,
On 09/11/17 14:02, Hendrik Leppkes wrote:
> On Thu, Nov 9, 2017 at 1:21 PM, James Cowgill wrote:
>> In commit 061a0c14bb57 ("decode: restructure the core decoding code"), the
>> deprecated avcodec_decode_* APIs were reworked so that they called into the
>> new avcodec_send_packet / avcodec_receive_frame API. This had the side effect
>> of prohibiting sending new packets containing data after a drain
>> packet, but in previous versions of FFmpeg this "worked" and some
>> applications relied on it.
>>
>> To restore some compatibility, reset the codec if we receive a new non-drain
>> packet using the old API after draining has completed. While this does
>> not give the same behaviour as the old API did, in the majority of cases
>> it works and it does not require changes to any other part of the decoding
>> code.
>>
>> Fixes ticket #6775
>> Signed-off-by: James Cowgill
>> ---
>> libavcodec/decode.c | 5 +
>> 1 file changed, 5 insertions(+)
>>
>> diff --git a/libavcodec/decode.c b/libavcodec/decode.c
>> index 86fe5aef52..2f1932fa85 100644
>> --- a/libavcodec/decode.c
>> +++ b/libavcodec/decode.c
>> @@ -726,6 +726,11 @@ static int compat_decode(AVCodecContext *avctx, AVFrame
>> *frame,
>>
>> av_assert0(avci->compat_decode_consumed == 0);
>>
>> +if (avci->draining_done && pkt && pkt->size != 0) {
>> +av_log(avctx, AV_LOG_WARNING, "Got unexpected packet after EOF\n");
>> +avcodec_flush_buffers(avctx);
>> +}
>> +
>
> I don't think this is a good idea. Draining and not flushing
> afterwards is a bug in the calling code, and even before recent
> changes it would result in inconsistent behavior and even crashes
> (with select decoders).
I am fully aware that this will only trigger if the calling code is
buggy. I am trying to avoid silent breakage of those applications doing
this when upgrading to ffmpeg 3.4.
I was looking at the documentation of avcodec_decode_* recently because
of this and I had some trouble deciding if using the API this way was
incorrect. I expect the downstreams affected thought that what they were
doing was fine and then got angry when ffmpeg suddenly "broke" their
code. This patch at least allows some sort of "transitional period"
until downstreams update.
From the perspective of Debian, I could either apply this patch to
ffmpeg, or I would have to go through over 100 reverse dependencies to
see if they abuse the API and then fix them. I currently know of two
(gst-libav1.0 and kodi), but there could be more - especially within
less used packages.
Thanks,
James
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Re: [FFmpeg-devel] [PATCH] lavc: reset codec on receiving packet after EOF in compat_decode
Le nonidi 19 brumaire, an CCXXVI, Derek Buitenhuis a écrit : > Is it more sensible to actually return an error here? Otherwise it's just > enabling > future incorrect code; API users tend to ignore stderr warnings. I guess an > argument > could be made both ways. Actually, if the use of the API is clearly wrong, then an immediate crash with an assert failure would be even better, IMHO, because it cannot be ignored. But if there is code out there doing it, then a soft transition with a warning would be in order. Regards, -- Nicolas George signature.asc Description: Digital signature ___ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
Re: [FFmpeg-devel] [PATCH] lavc: reset codec on receiving packet after EOF in compat_decode
On 11/9/2017 12:21 PM, James Cowgill wrote:
> +if (avci->draining_done && pkt && pkt->size != 0) {
> +av_log(avctx, AV_LOG_WARNING, "Got unexpected packet after EOF\n");
> +avcodec_flush_buffers(avctx);
> +}
Is it more sensible to actually return an error here? Otherwise it's just
enabling
future incorrect code; API users tend to ignore stderr warnings. I guess an
argument
could be made both ways.
- Derek
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Re: [FFmpeg-devel] [PATCH] lavc: reset codec on receiving packet after EOF in compat_decode
On Thu, Nov 9, 2017 at 1:21 PM, James Cowgill wrote:
> In commit 061a0c14bb57 ("decode: restructure the core decoding code"), the
> deprecated avcodec_decode_* APIs were reworked so that they called into the
> new avcodec_send_packet / avcodec_receive_frame API. This had the side effect
> of prohibiting sending new packets containing data after a drain
> packet, but in previous versions of FFmpeg this "worked" and some
> applications relied on it.
>
> To restore some compatibility, reset the codec if we receive a new non-drain
> packet using the old API after draining has completed. While this does
> not give the same behaviour as the old API did, in the majority of cases
> it works and it does not require changes to any other part of the decoding
> code.
>
> Fixes ticket #6775
> Signed-off-by: James Cowgill
> ---
> libavcodec/decode.c | 5 +
> 1 file changed, 5 insertions(+)
>
> diff --git a/libavcodec/decode.c b/libavcodec/decode.c
> index 86fe5aef52..2f1932fa85 100644
> --- a/libavcodec/decode.c
> +++ b/libavcodec/decode.c
> @@ -726,6 +726,11 @@ static int compat_decode(AVCodecContext *avctx, AVFrame
> *frame,
>
> av_assert0(avci->compat_decode_consumed == 0);
>
> +if (avci->draining_done && pkt && pkt->size != 0) {
> +av_log(avctx, AV_LOG_WARNING, "Got unexpected packet after EOF\n");
> +avcodec_flush_buffers(avctx);
> +}
> +
I don't think this is a good idea. Draining and not flushing
afterwards is a bug in the calling code, and even before recent
changes it would result in inconsistent behavior and even crashes
(with select decoders).
- Hendrik
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[FFmpeg-devel] [PATCH] lavc: reset codec on receiving packet after EOF in compat_decode
In commit 061a0c14bb57 ("decode: restructure the core decoding code"), the
deprecated avcodec_decode_* APIs were reworked so that they called into the
new avcodec_send_packet / avcodec_receive_frame API. This had the side effect
of prohibiting sending new packets containing data after a drain
packet, but in previous versions of FFmpeg this "worked" and some
applications relied on it.
To restore some compatibility, reset the codec if we receive a new non-drain
packet using the old API after draining has completed. While this does
not give the same behaviour as the old API did, in the majority of cases
it works and it does not require changes to any other part of the decoding
code.
Fixes ticket #6775
Signed-off-by: James Cowgill
---
libavcodec/decode.c | 5 +
1 file changed, 5 insertions(+)
diff --git a/libavcodec/decode.c b/libavcodec/decode.c
index 86fe5aef52..2f1932fa85 100644
--- a/libavcodec/decode.c
+++ b/libavcodec/decode.c
@@ -726,6 +726,11 @@ static int compat_decode(AVCodecContext *avctx, AVFrame
*frame,
av_assert0(avci->compat_decode_consumed == 0);
+if (avci->draining_done && pkt && pkt->size != 0) {
+av_log(avctx, AV_LOG_WARNING, "Got unexpected packet after EOF\n");
+avcodec_flush_buffers(avctx);
+}
+
*got_frame = 0;
avci->compat_decode = 1;
--
2.15.0
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