Right, exactly that way I tried it. However, I assumed that av_seek_frame
with flag AVSEEK_FLAG_BACKWARD set should seek to the previous I-frame. Am I
wrong here? If av_seek_frame doesn't work like I thought, is there another
libav function to achieve this?
On Jun 26, 2009, at 10:57 AM, Mediasystems GmbH wrote:
> Hello,
>
> I use ffmpeg for about one year with MPEG-2 streams. Everything
> works fine
> so far. Now I want to use H.264 coded videos as well. I'm trying to
> do a
> frame accurate random seeking on H.264 video streams. But I cannot
> accomplish to decode all single frames without any artefacts after
> calling
> av_seek_frame. If I go through the stream from the beginning, it
> works. Is
> it generally possible to do frame accurate seeking on H.264 video
> streams
> and how?
I think for this you need to seek to an I-frame, as H.264 is a
progressive encoder, and some of the frames only contain the changes
from the last frame to the current one. Once you have the previous I-
frame, you can then keep grabbing and decoding frames until you reach
the desired frame. This is how I was able to implement frame seeking
in one of my simple projects from a while ago.
>
> Code snippet:
>
> ret = av_seek_frame(pFormatCtx, videoStreamIndex, timestamp,
> AVSEEK_FLAG_BACKWARD); avcodec_flush_buffers(pCodecCtx);
>
> ...
> while (av_read_frame(pFormatCtx, pPacket) >= 0) { ...
> bytesDecoded = avcodec_decode_video(pCodecCtx, pFrame, ref
> frameFinished, packet.data, packet.size); ...
>
>
> Any help would be appreciated!
> Many thanks.
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