Re: [FFmpeg-devel] [PATCH 1/2] avcodec/parser: fix fetch_timestamp in a scenario with unaligned packets

2024-02-23 Thread Nicolas Gaullier 
>De : ffmpeg-devel  De la part de Michael 
>Niedermayer
>Envoyé : mercredi 21 février 2024 05:32
>On Tue, Feb 20, 2024 at 05:33:01PM +0100, Nicolas Gaullier wrote:
>> Fix fetch_timestamp when the frame start is in a previous packet.
>> 
>> Signed-off-by: Nicolas Gaullier 
>> ---
>>  libavcodec/parser.c | 6 +++---
>>  1 file changed, 3 insertions(+), 3 deletions(-)
>
>This change looses pts

I missed it : some broken streams are missing the zero_byte which makes the 
current h264 parser code to borrow a terminating null byte in the previous 
frame if available.
It seems there is currently no issue with that behaviour, but with my patch 
fixing the fetch_timestamp mechanism, it becomes one.
So, what is somewhat tricky is to guess if we are facing a broken stream or a 
conformant stream which actually has its zero_byte in the previous frame.
In my experience (including the sample from Michael and a sample of mine where 
there is no available null byte at the end of the frame),
the "usual broken streams" are missing the zero_byte for the first NAL unit 
which is an AUD, but the following NAL still has this zero_byte.
The following patch is a proposal to detect and overcome such a situation:
https://patchwork.ffmpeg.org/project/ffmpeg/list/?series=10877
At the end, this patch is required to handle broken streams and thus prepare 
the ground for the fetch_timestamp patch.

Another option would be for example to handle the data_alignment_indicator in 
the mpegts demuxer to force the alignment (ex: with a parser state reset),
but it seems it would involve some big unhappy changes in the code, with demux 
and parser tied together. Moreover, I don't think it is reliable and there 
might exists
broken stream with unaligned packets that we would still like to support.

Any inputs concerning broken streams for other codecs is welcome. For example, 
it may be required to handle broken hevc streams alike h264 ones: I have no 
opinion/ samples for that matter.

Nicolas
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Re: [FFmpeg-devel] [PATCH 1/2] avcodec/parser: fix fetch_timestamp in a scenario with unaligned packets

2024-02-20 Thread Michael Niedermayer 
On Tue, Feb 20, 2024 at 05:33:01PM +0100, Nicolas Gaullier wrote:
> Fix fetch_timestamp when the frame start is in a previous packet.
> 
> Signed-off-by: Nicolas Gaullier 
> ---
>  libavcodec/parser.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)

This change looses pts

--- /tmp/old2024-02-21 05:21:13.201646780 +0100
+++ /tmp/new2024-02-21 05:20:52.205417887 +0100
@@ -1,174 +1,172 @@
 [mpegts  read_frame_internal stream=2, pts=310332330, dts=310332330, 
size=49072, duration=0, flags=0
-[mpegts  read_frame_internal stream=2, pts=310348800, dts=310348800, 
size=16516, duration=0, flags=0
-[mpegts  read_frame_internal stream=2, pts=310356000, dts=310356000, 
size=16876, duration=0, flags=0
-[mpegts  read_frame_internal stream=2, pts=310366800, dts=310366800, 
size=51652, duration=0, flags=0
-[mpegts  read_frame_internal stream=2, pts=310363200, dts=NOPTS, size=15588, 
duration=0, flags=0
-[mpegts  read_frame_internal stream=2, pts=310370400, dts=NOPTS, size=21476, 
duration=0, flags=0
-[mpegts  read_frame_internal stream=2, pts=310402800, dts=NOPTS, size=276868, 
duration=3600, flags=1
-[mpegts  read_frame_internal stream=2, pts=310388400, dts=NOPTS, size=85884, 
duration=3600, flags=0
-[mpegts  read_frame_internal stream=2, pts=310381200, dts=NOPTS, size=45761, 
duration=3600, flags=0
+[mpegts  read_frame_internal stream=2, pts=NOPTS, dts=NOPTS, size=16516, 
duration=0, flags=0
+[mpegts  read_frame_internal stream=2, pts=310348800, dts=310348800, 
size=16876, duration=0, flags=0
+[mpegts  read_frame_internal stream=2, pts=310356000, dts=310356000, 
size=51652, duration=0, flags=0
+[mpegts  read_frame_internal stream=2, pts=310366800, dts=310366800, 
size=15588, duration=0, flags=0
+[mpegts  read_frame_internal stream=2, pts=310363200, dts=NOPTS, size=21476, 
duration=0, flags=0
+[mpegts  read_frame_internal stream=2, pts=310370400, dts=NOPTS, size=276868, 
duration=3600, flags=1
+[mpegts  read_frame_internal stream=2, pts=NOPTS, dts=NOPTS, size=85884, 
duration=3600, flags=0
+[mpegts  read_frame_internal stream=2, pts=310388400, dts=NOPTS, size=45761, 
duration=3600, flags=0


[...]
-- 
Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

"You are 36 times more likely to die in a bathtub than at the hands of a
terrorist. Also, you are 2.5 times more likely to become a president and
2 times more likely to become an astronaut, than to die in a terrorist
attack." -- Thoughty2



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[FFmpeg-devel] [PATCH 1/2] avcodec/parser: fix fetch_timestamp in a scenario with unaligned packets

2024-02-20 Thread Nicolas Gaullier 
Fix fetch_timestamp when the frame start is in a previous packet.

Signed-off-by: Nicolas Gaullier 
---
 libavcodec/parser.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/libavcodec/parser.c b/libavcodec/parser.c
index efc28b8918..853b5323b0 100644
--- a/libavcodec/parser.c
+++ b/libavcodec/parser.c
@@ -153,11 +153,11 @@ int av_parser_parse2(AVCodecParserContext *s, 
AVCodecContext *avctx,
 }
 
 if (s->fetch_timestamp) {
-s->fetch_timestamp = 0;
 s->last_pts= s->pts;
 s->last_dts= s->dts;
 s->last_pos= s->pos;
-ff_fetch_timestamp(s, 0, 0, 0);
+ff_fetch_timestamp(s, FFMIN(s->fetch_timestamp, 0), 0, 0);
+s->fetch_timestamp = 0;
 }
 /* WARNING: the returned index can be negative */
 index = s->parser->parser_parse(s, avctx, (const uint8_t **) poutbuf,
@@ -179,7 +179,7 @@ int av_parser_parse2(AVCodecParserContext *s, 
AVCodecContext *avctx,
 
 /* offset of the next frame */
 s->next_frame_offset = s->cur_offset + index;
-s->fetch_timestamp   = 1;
+s->fetch_timestamp   = index >= 0 ? 1 : index;
 } else {
 /* Don't return a pointer to dummy_buf. */
 *poutbuf = NULL;
-- 
2.30.2

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