On Mon, Oct 21, 2013 at 4:21 PM, Carl Eugen Hoyos <[email protected]> wrote: > Robert Krüger <krueger@...> writes: > >> If my debug output is correct, both contain no >> B-slices/frames (I just noticed that) but they >> do contain I-slices/frames. If I am not missing >> something, those I-Frames should be valid random >> access points then. > > Do you mean you debugged the sample (with a stream > analyzer) and you know that every I-frame is a > random access point or would you just expect every > I-frame in the sample being a random access point?
Not with a stream analyzer but by adding code to ffmpeg's h264 parser and reading the spec. Since only P- and I-slices are parsed (I can see that in the debug output), I would indeed expect every I-frame (meaning any frame only consisting of one I-slice in the stream) to be a valid access point or I am missing something (which may very well be the case). > > Testing the 720p sample, it appears to me that > FFmpeg thinks the first random access point after > the initial IDR frame is the 28th frame, a P-frame. What do you mean "thinks". Are you looking at the seeking code? Judging by the debug output of the h.264 parser I see that the packet with pts 79304 (it's the 27th packet from the start) contains an I-slice and is the only slice parsed from that packet, so I would say that this is indeed a self-contained I-frame (also the size/bitrate of that packet is an indication for it being an I slice). There is also an SPS at 79304. > If FFmpeg is right (and the 27th frame is no random > access point), how should the random access point > be signaled? You mean what criterion to use to decide it's a random access point? I naively thought, when only encountering P- and I-slices in the entire stream any picture that only consists of one I-slice could be considered a valid random access point especially with the coincidence that there seems to be an SPS directly before every I-slice in the stream but I am far from being an h264 expert and may be wrong. > > [...] > >> > Even better. Which commit are you talking about? > > Iirc, fixed ticket with keyword "h264". You mean 2738? Robert _______________________________________________ Libav-user mailing list [email protected] http://ffmpeg.org/mailman/listinfo/libav-user
