[Libav-user] AAC decode problems

[Anton Shekhovtsov]

2017-09-14 14:06 GMT+03:00 Info || Non-Lethal Applications <
info at non-lethal-applications.com>:

> Hi guys,
>
> I just received a movie file with AAC audio which doesn't play correctly
> in my player using the ffmpeg libraries.
> It sounded “robotic” and the audio ran out of sync rather quickly.
>
> Ffprobe output:
>
> ffprobe version 3.3.1 Copyright (c) 2007-2017 the FFmpeg developers
>   built with llvm-gcc 4.2.1 (LLVM build 2336.11.00)
>   configuration: --prefix=/Volumes/Ramdisk/sw --enable-gpl
> --enable-pthreads --enable-version3 --enable-libspeex --enable-libvpx
> --disable-decoder=libvpx --enable-libmp3lame --enable-libtheora
> --enable-libvorbis --enable-libx264 --enable-avfilter
> --enable-libopencore_amrwb --enable-libopencore_amrnb --enable-filters
> --enable-libgsm --enable-libvidstab --enable-libx265 --disable-doc
> --arch=x86_64 --enable-runtime-cpudetect
>   libavutil      55. 58.100 / 55. 58.100
>   libavcodec     57. 89.100 / 57. 89.100
>   libavformat    57. 71.100 / 57. 71.100
>   libavdevice    57.  6.100 / 57.  6.100
>   libavfilter     6. 82.100 /  6. 82.100
>   libswscale      4.  6.100 /  4.  6.100
>   libswresample   2.  7.100 /  2.  7.100
>   libpostproc    54.  5.100 / 54.  5.100
> Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '/Users/flo/Downloads/wetransfer-6ec47f/IQT
> Capture 170911 Unity Round1.mov':
>   Metadata:
>     major_brand     : qt
>     minor_version   : 512
>     compatible_brands: qt
>     encoder         : Lavf57.66.102
>   Duration: 00:07:58.81, start: 0.000000, bitrate: 2672 kb/s
>     Stream #0:0(eng): Video: h264 (High) (avc1 / 0x31637661), yuv420p,
> 1280x720, 2499 kb/s, 29.97 fps, 29.97 tbr, 30k tbn, 59.94 tbc (default)
>     Metadata:
>       handler_name    : DataHandler
>     Stream #0:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz,
> stereo, fltp, 162 kb/s (default)
>     Metadata:
>       handler_name    : DataHandler
>
> By examining the file I found out that the packet durations of the AAC
> stream were not 1024 as they are with all the other files I have but rather
> either 1000 or 1100.
> While this by itself would not be a problem, it’s very confusing that the
> AAC decoder outputs AVFrames with a duration of 1024.
>
> So now I’m a bit stuck as I really don’t know what to do.
> If the packets were all 1000 I would try discarding the last 24 samples of
> each AVFrame but as the frame apparently only holds 1024 samples although
> the packet says it contains 1100 samples, I’m stuck.
> I tried sending a NULL packet in the case of longer packets hoping to get
> the remains 76 samples out of the decoder but I got this error message:
>
> *[aac @ 0x10539da00] Got unexpected packet size after a partial decode*
>
> The file plays fine in both QuickTime and VLC so there must be a correct
> way of handling these kind of files..
>
> I’d be very grateful for any insight anyone of you might have!
>
> Thanks and best,
>
> Flo
>
> _______________________________________________
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> Libav-user at ffmpeg.org
> http://ffmpeg.org/mailman/listinfo/libav-user
>
>
What do you mean "packet contains 1100 samples", how is that specified?
AVPacket->duration is in time_base units, not in samples.
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