My case is live streaming.
I have tried it and definitely keyframes are not aligned between input
and output streams.
For all encoded output streams it is very simple to obtain alignement
with setting the fixed GOP size. But the PTS and keyframes of input are
never aligned with that.
Sometimes, PTS of the output streams are not aligned, and it seems that
encoding does not start "at the same time", like there is a delay to
startup different for different output streams. I have seen this very
often using the "tee" output
On 5/2/15 1:43 PM, Henk D. Schoneveld wrote:
On 02 May 2015, at 11:38, Anatol <anatol2...@gmail.com> wrote:
I don't think that 'keep source keyframes' might impose any a/v sync issues
that differ from any other encoding flows.
AFIAK, 'force_key_frames' acts on the output/encoding, it does not aware of
the decoding processing. For that matter - scene cuts are evaluated from
post-decoding/raw frames.
Did you try without thinking of alignment what happens ?
Take a source file of several minutes and do your encoding for several bitrates
with HLS and then test see if problems do really show up. Meaning maybe you try
to solve a potential problem, looking at recuirements, that in reality don’t
exist ?
On Sat, May 2, 2015 at 12:31 PM, Haris Zukanovic <
haris.zukanovi...@gmail.com> wrote:
My "simple" idea was that instead of deducing from a "formula" like
-force_key_frames 'expr:gte(t,n_forced*5)'
force_key_frames somehow took this kind of info directly from the input
stream and passed onto all output streams
This could be called something like
-force_key_frames 'from_source'
Do you think it is possible to do?
On 5/2/15 10:41 AM, Anatol wrote:
It does not matter the type of the incoming protocol.
And slight un-alignment tolerated by the CDN providers and Apple HLS
validation tools.
Therefore the source live stream can be used in an adaptive-bitrate sets,
IF the other streams match their key frames.
By the way Wowza has this option ("keep Source key frames") in its
Transcoder add-on.
But Wowza also has other problems ...
On Sat, May 2, 2015 at 11:06 AM, Henk D. Schoneveld <belca...@zonnet.nl>
wrote:
On 02 May 2015, at 06:27, Anatol <anatol2...@gmail.com> wrote:
The idea is to gain the option to use the H264 source stream along with
live transcoded streams in an adaptive bitrate delivery modes (HLS, HDS,
etc), that require aligned keyframes on ALL participating streams.
Could it be ALL, except the livestream itself ?
Or is the livestream also available via HLS ?
If yes, then you’ll have to encode this one as well.
This can only be achieved if the source stream is encoded with the same
version of the encoder you’re using your self. I can imagine that
different
encoders could behave slightly different.
BTW what is your source ? Is it predictable like DVB-S from the same
broadcaster ?
From the top of my head BBC broadcast has an I-frame every 12 or 13
frames.
Another potential issue could be the delay between the video and audio
stream, which would force you to also encode the source stream.
Hope it helps.
On Sat, May 2, 2015 at 2:48 AM, Henk D. Schoneveld <belca...@zonnet.nl>
wrote:
On 01 May 2015, at 20:43, Haris Zukanovic <haris.zukanovi...@gmail.com
wrote:
Indeed force-ing keyframes at certain positions is meant to keep
multiple
output encodings keyframe aligned. The input stream is already h264 in
our
case.
Moreover, if one could "copy" all iframe positions, and possibly also
all
other frametypes from the input stream there would not be any need for
scene detection if that was already done in the input stream. I am not
sure
how much heavy lookahead calculations and perhaps other heavy
calculations
could also be skipped?
What are you trying to achieve ? A performance boost ? I don’t think
that
you’ll achieve improvement worthwhile, if anything at all. The working
of
the encoder should need to be totally rewritten to make something like
this
happen at all. Encoding of a frame depends on former and following
frames,
the result I P or B frame is the result. Your source is h264 already,
so I
think you’ll rescale and re-encode to achieve that. The calculation has
to
be done. Knowing in advance that it will be en I P or B frame won’t make
any difference in the amount of calculations in my opinion.
On May 1, 2015 7:42 PM, "Henk D. Schoneveld" <belca...@zonnet.nl>
wrote:
On 01 May 2015, at 13:06, Haris Zukanovic <
haris.zukanovi...@gmail.com
wrote:
Is the decision about exactly which frame to make an IDR frame made
in
x264 or ffmpeg?
In general I-frames are placed at scene-changes, this can happen
random.
Additionally you can can force an I-frame every arbitrary amount of
frames
by specifying the gop-size. The function of an I-frame is to hold max
frame
info P and B frames build on that complete I-frame. It doesn’t make
sense
from an encoding viewpoint to skip an I-frame at a scene-change, it’s
just
impossible.
Adding more than ‘a minimum amount’ of I-frames only makes sense for
seeking purposes, at the cost of less compression/higher then
necessary
bitrate.
Any pointer or advice on where to look for this in the code?
On 4/29/15 8:54 PM, Anatol wrote:
No responses on that one?
It is very important issue.
On Mon, Apr 27, 2015 at 11:47 PM, Haris Zukanovic <
haris.zukanovi...@gmail.com> wrote:
Hello,
Can I use force_key_frames in some way to produce keyframes (IDR,
not
I-frames) at exactly the same PTS in output streams as they are
found
in
the live input stream? Both input and output are h264 and live
streaming.
Something analogous to using 2 pass encoding for VOD and in the
second
pass keyframes are inserted exactly where they are recorded in the
first
pass... Is that something like that even theoretically doable for
live
streaming?
thanx
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