On Mon, Jun 22, 2015 at 11:02 AM, wm4 <nfx...@googlemail.com> wrote: > On Sun, 21 Jun 2015 18:34:33 -0400 > "Ronald S. Bultje" <rsbul...@gmail.com> wrote: > >> Hi, >> >> On Sun, Jun 21, 2015 at 5:17 PM, Hendrik Leppkes <h.lepp...@gmail.com> >> wrote: >> >> > On Sun, Jun 21, 2015 at 10:41 PM, Ronald S. Bultje <rsbul...@gmail.com> >> > wrote: >> > > --- >> > > libavformat/yuv4mpeg.h | 1 + >> > > libavformat/yuv4mpegdec.c | 26 +++++++++++++++++++------- >> > > 2 files changed, 20 insertions(+), 7 deletions(-) >> > > >> > >> > What happens if a seek does not end up on a perfect frame boundary? >> > Wouldn't that entirely screw over any further reading? >> > >> > So is it really that "rough", or does it actually work precise enough >> > to do that? >> >> >> It works for all y4m files I see in the wild, but the problem is that the >> y4m spec is a little confusing. The frame header magic is "FRAME", followed >> by optional per-frame options, and then a "\n". This is always empty (i.e. >> "FRAME\n"), but in theory it could be non-empty and then this doesn't work. >> >> I don't know how much we care about such theoretical files to make a more >> difficult dur/seek implementation. > > Why not use generic seeking mode? Add AVFMT_GENERIC_INDEX to the format > flags. The utils.c will do seeking by doing byte seeks and using the > byte position of previous packets. If you seek forward, it will read > and skip packets until the target is reached (for parts of the file > that have not been indexed yet). This should be very reliable, but of > course seek speed will depend on I/O bandwidth.
Generic seeking is rather expensive, and if a format is already strict CBR, doing a seek based on that is probably better. I wonder how hard it would be to write a re-sync function to find the next FRAME header when a seek does actually end up on the wrong spot. - Hendrik _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
