id,summary,reporter,owner,description,type,status,priority,component,version,resolution,keywords,cc,blockedby,blocking,reproduced,analyzed
9248,FFplay does not try to guess channel layout for stereo wav-files with WAVE_FORMAT_PCM header,CoRoNe,,"Creating the test file:
{{{
ffmpeg -f lavfi -i aevalsrc='sin(864*2*PI*t):c=stereo:d=3' aevalsrc.wav
}}}
Opening '`aevalsrc.wav`' with `ffmpeg` you'll see:
{{{
ffmpeg -i aevalsrc.wav
[...]
Guessed Channel Layout for Input Stream #0.0 : stereo
}}}
This wav-file doesn't have a channel-layout-tag, so `ffmpeg` tries to guess it and sets the channel layout to stereo in this case. In order for `ffmpeg` not having to guess, you can manually specify `-channel_layout stereo`, which has the same outcome.
The channel layout is now set, which `ffmpeg` reports (with a more verbose loglevel) as:
{{{
[graph_0_in_0_0 @ xxx] [...] chlayout:0x3
}}}

With `ffplay` however this is not the case. It does play '`aevalsrc.wav`', but also reports:
{{{
ffplay -v 40 aevalsrc.wav
[...]
[ffplay_abuffer @ xxx] [...] chlayout:(null)
}}}
According to the docs `ffplay` ''should'' have a `-channel_layout` option...
{{{
ffplay --help | grep ""\-channel_layout""
  -channel_layout    <uint64>     ED..A...... (from 0 to 1.84467e+19) (default 0)
}}}
...but that somehow doesn't work:
{{{
ffplay -channel_layout stereo aevalsrc.wav
[...]
[pcm_s16le @ xxx] [Eval @ 05a6f2cc] Undefined constant or missing '(' in 'stereo'
[pcm_s16le @ xxx] Unable to parse option value ""stereo""
[pcm_s16le @ xxx] Error setting option channel_layout to value stereo.
}}}
''""The wav-file plays, so what's the problem?""'', you might say. Problems start to occur however when audio-filters are applied, like changing the tempo and pitch for instance:
{{{
ffplay -af ""asetrate=22050"" aevalsrc.wav
[...]
[auto_resampler_0 @ xxx] Cannot select channel layout for the link between filters auto_resampler_0 and Parsed_asetrate_0.
[auto_resampler_0 @ xxx] Unknown channel layouts not supported, try specifying a channel layout using 'aformat=channel_layouts=something'.
}}}
Using the ""`aformat`""-filter, `-af ""aformat=cl=stereo,asetrate=22050""`, obviously works, though the channel layout is still unknown:
{{{
[ffplay_abuffer @ xxx] [...] chlayout:(null)
}}}

I don't understand however why `-af ""aformat=cl=stereo""` is necessary for `ffplay`, why `-channel_layout stereo` doesn't work and why in the first place it doesn't try to guess the channel layout like `ffmpeg` does.

The only way I've found to play the wav-file with `ffplay` without the need for `-af ""aformat=cl=stereo""` is to open '`aevalsrc.wav`' with Audacity and save it as a wav-file with a WAVEX (WAVE_FORMAT_EXTENSIBLE) header. That way `ffplay` does recognize the channel layout:
{{{
[ffplay_abuffer @ xxx] [...] chlayout:0x3
}}}
Why with Audacity? Because of '`libavformat/riffenc.c`'...
{{{#!c lineno=79 marks=81
    waveformatextensible = (par->channels > 2 && par->channel_layout) ||
                           par->channels == 1 && par->channel_layout && par->channel_layout != AV_CH_LAYOUT_MONO ||
                           par->channels == 2 && par->channel_layout && par->channel_layout != AV_CH_LAYOUT_STEREO ||
                           par->sample_rate > 48000 ||
                           par->codec_id == AV_CODEC_ID_EAC3 ||
                           av_get_bits_per_sample(par->codec_id) > 16;
}}}
...I believe `ffmpeg` never saves stereo audio streams as wav-files with a WAVEX header. And as far as I know there's no way to force that.",defect,closed,normal,ffplay,git-master,fixed,ffplay,CoRoNe,,,0,0