On Fri, 21 Oct 2016 16:59:14 +0100 Derek Buitenhuis <derek.buitenh...@gmail.com> wrote:
> On 10/21/2016 4:32 PM, Derek Buitenhuis wrote: > > * Audio packets. Especially audio packets with a large number of > > samples. > > It's extremely likely that edits will not fall on packet boundaries, > > and > > depending on the number of samples per packet, audio sync issues can > > and > > will occur, even with smaller packets of e.g. 1024 samples, if there > > are > > a large number of entries in the edit list. Gradual loss of sync will > > occur. > > Apologies, I do see skip_samples is used, but it's unclear if it is correct > or how to use it. > > i.e. skip_samples is documented as: > > "Number of samples to skip at the start of the frame decoded from the > next packet." > > It's extremely vague, doesn't really say *when* to discard samples. After > start? After a seek? Every packet? Does skip_samples get updated mid-demux? > > I've been told it's after every reset (i.e. call to av_codec_flush), but the > docs > sure don't seem to say this... In practice, it seems skip_samples is a counter that can affect all decoded frames after it has been set. This can be by the user along with a av_codec_flush call, or by a packet due to packet side data like AV_PKT_DATA_SKIP_SAMPLES (or with the new edit list code, the discard flag). I think logically, the side data sets skip_samples _before_ the output of the corresponding packet is decoded, but _after_ the previous packet is decoded. Once skip_samples has reached 0, it has no effect on any decoded data anymore. (What annoys me here is that not all decoders do 1:1 packet in/out, but may do arbitrary things like variable buffering of packets. All this means that avctx->internal->pkt can be set to a random packet, while this edit list logic requires that it's the "current" packet.) > Also a friendly reminder that users may not be using libavcodec, but their own > decoder. Indeed, this would mean all those users have to replicate the hacks in libavcodec/utils.c to get not garbage with libavformat-demuxed mp4s containing edit lists. _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
