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decoder/ffmepg: fill AudioFormat from AVCodecContext, not AVCodecParameters 

`AVCodecParameters` contains values from the codec detected by
avformat_find_stream_info(), but after avcodec_open2(), a different
codec might be selected with a different `AVSampleFormat`.  This leads
to misinterpretation of data returned from FFmpeg, leading to random
noise or silence.

This was observed with FFmpeg 4.0.2 and a TS container file containing
MP2.  A mp3-float codec was detected returning `AV_SAMPLE_FMT_FLTP`,
but finally the `mpegaudiodec_fixed.c` was used, returning
`AV_SAMPLE_FMT_S16`.

By using the audio format from `AVCodecContext`, we ensure that MPD
and FFmpeg always agree on the actual audio format in the buffer.

This removes the FFmpeg bug workaround from commit e1b032cbad which I
assume is obsolete after 7 years.

Fixes #380
This commit is contained in:
Max Kellermann 2018-11-04 22:30:50 +01:00
parent bd115a4008
commit 6c602811df
2 changed files with 12 additions and 16 deletions
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1
NEWS
View File

@ -1,6 +1,7 @@
ver 0.21.2 (not yet released)
* decoder
- ffmpeg: require FFmpeg 3.1 or later
- ffmpeg: fix broken sound with certain codecs
ver 0.21.1 (2018/11/04)
* protocol

27
src/decoder/plugins/FfmpegDecoderPlugin.cxx
View File

@ -556,28 +556,23 @@ FfmpegDecode(DecoderClient &client, InputStream &input,
avcodec_parameters_to_context(codec_context, av_stream.codecpar);
const SampleFormat sample_format =
ffmpeg_sample_format(GetSampleFormat(codec_params));
if (sample_format == SampleFormat::UNDEFINED) {
// (error message already done by ffmpeg_sample_format())
return;
}
const auto audio_format = CheckAudioFormat(codec_params.sample_rate,
sample_format,
codec_params.channels);
/* the audio format must be read from AVCodecContext by now,
because avcodec_open() has been demonstrated to fill bogus
values into AVCodecContext.channels - a change that will be
reverted later by avcodec_decode_audio3() */
const int open_result = avcodec_open2(codec_context, codec, nullptr);
if (open_result < 0) {
LogError(ffmpeg_domain, "Could not open codec");
return;
}
const SampleFormat sample_format =
ffmpeg_sample_format(codec_context->sample_fmt);
if (sample_format == SampleFormat::UNDEFINED) {
// (error message already done by ffmpeg_sample_format())
return;
}
const auto audio_format = CheckAudioFormat(codec_context->sample_rate,
sample_format,
codec_context->channels);
const SignedSongTime total_time =
av_stream.duration != (int64_t)AV_NOPTS_VALUE
? FromFfmpegTimeChecked(av_stream.duration, av_stream.time_base)