> On Feb 23, 2021, at 2:42 PM, Marton Balint <c...@passwd.hu> wrote: > > > > On Sat, 20 Feb 2021, Dave Rice wrote: > >> Hi, >> >>> On Oct 31, 2020, at 5:15 PM, Marton Balint <c...@passwd.hu >>> <mailto:c...@passwd.hu>> wrote: >>> On Sat, 31 Oct 2020, Dave Rice wrote: >>>>> On Oct 31, 2020, at 3:47 PM, Marton Balint <c...@passwd.hu >>>>> <mailto:c...@passwd.hu>> wrote: >>>>> On Sat, 31 Oct 2020, Dave Rice wrote: >>>>>> Hi Marton, >>>>>>> On Oct 31, 2020, at 12:56 PM, Marton Balint <c...@passwd.hu >>>>>>> <mailto:c...@passwd.hu>> wrote: >>>>>>> Fixes out of sync timestamps in ticket #8762. >>>>>> Although Michael’s recent patch does address the issue documented in >>>>>> 8762, I haven’t found this patch to fix the issue. I tried with -c:a >>>>>> copy and with -c:a pcm_s16le with some sample files that exhibit this >>>>>> issue but each output was out of sync. I put an output at >>>>>> https://gist.github.com/dericed/659bd843bd38b6f24a60198b5e345795 >>>>>> <https://gist.github.com/dericed/659bd843bd38b6f24a60198b5e345795>. That >>>>>> output notes that 3597 packages of video are read and 3586 packets of >>>>>> audio. In the resulting file, at the end of the timeline the audio is 9 >>>>>> frames out of sync and my output video stream is 00:02:00.020 and output >>>>>> audio stream is 00:01:59.653. >>>>>> Beyond copying or encoding the audio, are there other options I should >>>>>> use to test this? >>>>> Well, it depends on what you want. After this patch you should get a file >>>>> which has audio packets synced to video, but the audio stream is sparse, >>>>> not every video packet has a corresponding audio packet. (It looks like >>>>> our MOV muxer does not support muxing of sparse audio therefore does not >>>>> produce proper timestamps. But MKV does, please try that.) >>>>> You can also make ffmpeg generate the missing audio based on packet >>>>> timestamps. Swresample has an async=1 option, so something like this >>>>> should get you synced audio with continous audio packets: >>>>> ffmpeg -y -i 1670520000_12.dv -c:v copy \ >>>>> -af aresample=async=1:min_hard_comp=0.01 -c:a pcm_s16le 1670520000_12.mov >>>> Thank you for this. With the patch and async, the result is synced and the >>>> resulting audio was the same as Michael’s patch. >>>> Could you explain why you used min_hard_comp here? IIUC min_hard_comp is a >>>> set a threshold between the strategies of trim/fill or stretch/squeeze to >>>> align the audio to time; however, the async documentation says "Setting >>>> this to 1 will enable filling and trimming, larger values represent the >>>> maximum amount in samples that the data may be stretched or squeezed” so I >>>> thought that async=1 would not permit stretch/squeeze anyway. >>> It is documented poorly, but if you check the source code you will see that >>> async=1 implicitly sets min_comp to 0.001 enabling trimming/dropping. >>> min_hard_comp decides the threshold when silence injection actually >>> happens, and the default for that is 0.1, which is more than a frame, >>> therefore not acceptable if we want to maintain <1 frame accuracy. Or at >>> least that is how I think it should work. >> > >> I’ve found that aresample=async=1:min_hard_comp=0.01, as discussed here, >> works well to add audio samples to maintain timestamp accuracy when muxing >> into a format like mov. However, this approach doesn’t work if the >> sparseness of the audio stream is at the end of the stream. Is there a way >> to use min_hard_comp to consider differences between a timestamp and audio >> data when one of the ends of that range is the end of the file? > > I am not aware of a smart method to generate missing audio in the end until > the end of video. > > As a possible workaround you may query the video length using > ffprobe or mediainfo, and then use a second filter, apad to pad audio: > > -af aresample=async=1:min_hard_comp=0.01,apad=whole_dur=<video_length> > > Tnis might do what you want, but requires an additional step to query the > video length…
[…] Perfect, thanks for sharing this idea. Dave _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
