Le 28 mars 2014 à 22:04, wm4 <[email protected]> a écrit : > On Fri, 28 Mar 2014 21:19:55 +0100 > Lucas Soltic <[email protected]> wrote: > >> Hello! >> >> Does av_frame_get_best_effort_timestamp() gives a PTS or DTS? >> >> At first I would have thought it's a PTS, because it's impossible for >> decoding to correctly happen if DTS does not exist in the packet, but then I >> read that the packet DTS may be AV_NOPTS_VALUE (DTS being a NOPTS..??!). If >> that is correct, is there a reliable way to know the DTS too (in the core >> meaning of DTS, even if the file does not set it)? > > Some files have PTS and DTS mixed (mpeg mostly), some files have PTS > only (e.g. Matroska), some files have DTS only (e.g. AVI). The general > solution is to use DTS if PTS is set to NOPTS. > > Here's how av_frame_get_best_effort_timestamp() is calculated: > > https://git.videolan.org/?p=ffmpeg.git;a=blob;f=libavcodec/utils.c;h=b43f67540e834d45058f9d694cc6c090d1b4c27d;hb=HEAD#l1995 > > Looks complicated, but is rather simple. As I understand, this is > mostly a workaround if PTS or DTS are set incorrectly. > > > This function takes AVFrame.pkt_pts and AVFrame.pkt_dts as inputs. It > returns what will be used as AVFrame.best_effort_timestamp. What this > function does is: > > 1. count how often it happens that PTS or DTS are not monotonic > (normally, the DTS _and_ PTS should not decrease after the decoder; > this is not true _before_ the decoder, but the decoder should > reorder them so that they're monotonic, and some broken files might > violate this) > 2. if PTS is more often wrong than DTS, use the DTS as output timestamp > > Libav does not have the AVFrame.best_effort_timestamp field. Butthe > Libav command line tools (avplay, avconv) calculates it the same way: > > https://git.libav.org/?p=libav.git;a=blob;f=cmdutils.c;h=69a11bdd4fb33ccdc1420e15edb7c47c8ce84098;hb=HEAD#l1431 > > And that's why I would recommend just copying the code. It's trivial > anyway, at least once you understand it, and your project will be > compatible to both FFmpeg and Libav. > _______________________________________________ > Libav-user mailing list > [email protected] > http://ffmpeg.org/mailman/listinfo/libav-user
Thanks for all your answers :) So... to sum it up, some formats have DTS or PTS or both. I guess no file has none? Then if I want to seek, I saw that some demuxers seek by PTS, others by DTS, depending on whether AVFMT_SEEK_TO_PTS is set. If the format only has DTS, will AVFMT_SEEK_TO_PTS never be set? If the format only has PTS, will AVFMT_SEEK_TO_PTS always be set? If AVFMT_SEEK_TO_PTS is set, are the PTS provided by the format reliable? If AVFMT_SEEK_TO_PTS is not set, are the DTS provided by the format reliable? Lucas _______________________________________________ Libav-user mailing list [email protected] http://ffmpeg.org/mailman/listinfo/libav-user
