[Libav-user] Reducing latency of file opening (when playing from http)
kalileo at universalx.net
Sun May 12 22:17:45 CEST 2013
On May 12, 2013, at 22:43 , Carl Eugen Hoyos wrote:
> Kalileo <kalileo at ...> writes:
>> This is also what I noticed, when playing with
>> probesize and analyzeduration trying to get the
>> player to start more quickly (using mpegts
>> (h264/aac) streams served through a memory buffer).
> Since I did not really understand the paragraph I cut:
> Do you mean that although you used -probesize and
> -analyzeduration, the time to probe a file did not
That was my impression, yes.
> If yes, this sounds like a serious bug that should be
> (Needs command line, console output etc.)
I'm not talking about ffmpeg command line, but about using the ffmpeg libraries in own code.
>> This leads to the question why does a known stream
> (What is a "known" stream?)
That is a stream from which I know exactly all parameters, codecs, container, all details.
Which means I should be able to set these details, instead of probing them.
>> need to get probed / analyzed at all?
> I may miss something but I wonder how you want to
> demux a transport stream without some probing /
> there are many tickets from people who miss their
> subtitle streams when opening their file…
Sure, however if it is a stream which I created, encoded, then I should not need to probe, I know already how I encoded it.
> Additionally, user streams without PAT and/or PMT
> are not unusual (there used to be a bug in *zap
> for many years), so careful probing in transport
> streams is particularly important afaict.
Yes, understood. The streams I'm using do have PAT/PMT, and the first chunk of the stream which I feed to the player always starts with PAT/PMT, and the first video frame after that is a key frame.
Therefore I think it should be possible to manually set all what avformat_find_stream_info is setting, and to skip feeding the stream to avformat_find_stream_info.
In my case the input is mpegts in chunks starting with PAT/PMT, which I encode myself, so I know all encoding details. The steps are:
avformat_find_stream_info() <== this should be not needed if I set all required codec params.
and then for video and again for audio:
However if I don't run avformat_find_stream_info() it sometimes works and sometimes not. Obviously I miss something what avformat_find_stream_info() is doing.
Just to avoid any misunderstanding, it all works fine, and now I try to optimize it, to speed it up, and to avoid the delay caused by avformat_find_stream_info() by removing the requirement to run it.
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