[gst-devel] gst-ffmpeg : waiting_for_key condition problem in dec (newsegement handling)

[Antoine Tremblay]

Hi all,

I think there's a problem with the way the newsegment event in handled in
gstffmpecdec.c
in : gst_ffmpegdec_sink_event (GstPad * pad, GstEvent * event) (in HEAD)

I see : case GST_EVENT_NEWSEGMENT: { ....

if (ffmpegdec->opened) {
avcodec_flush_buffers (ffmpegdec->context);

if (ffmpegdec->context->codec_id == CODEC_ID_MPEG2VIDEO ||
ffmpegdec->context->codec_id == CODEC_ID_MPEG4 ||
ffmpegdec->context->codec_id == CODEC_ID_H264) {
ffmpegdec->waiting_for_key = TRUE;
}
}
ffmpegdec->waiting_for_key = TRUE;

With this code waiting_for_key will always be set to TRUE ... so why is
there the condition with the codecs_ids ? and why is it set to true when
it's most codecs don't require it ? I guessed since these formats could be
streamed the waiting_for_key should be false there and there should be an
other conditions so that the second isn't executed...

Or it's the opposite while it's not opened waiting_for_key should be false
and then set true when opened for the selected codecs... That would be more
logical and I think that's the way to do it but i'm just wondering why then
would someone have placed MPEG4 and H264 there when they don't need a
keyframe...?

To me this should be written like :


if (ffmpegdec->opened) {
avcodec_flush_buffers (ffmpegdec->context);

if (ffmpegdec->context->codec_id == CODEC_ID_MPEG2VIDEO || other coded which
requires keyframes )
ffmpegdec->waiting_for_key = TRUE;
}
else {
ffmpegdec->waiting_for_key = FALSE;
}
}
else {
ffmpegdec->waiting_for_key = FALSE;
}

Note that I realise this might be done so that when seeking you directly get
a keyframe ,, but since newsegment is always sent before the 1st buffer is
sent it has the effect that waiting_for_key is always set to TRUE at 1st ..
so if you have a stream with 1 keyframe at start and then no other keyframes
you will never be able to play it if you start at frame 2, even if you
should be able to and do we really need to get a keyframe direclty ?

Thanks a lot

Antoine
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