2.1 regression: avcodec audio encoder divides by zero

This command:

vlc --no-sout-video music.mp3 --sout '#transcode{acodec=ulaw,rate=8000,channels=1}:display' -vv

results in:

[0xad233340] main input debug: Decoder buffering done in 585 ms

Program received signal SIGFPE, Arithmetic exception.
[Switching to Thread 0xabaf9b40 (LWP 15088)]
0xadc0e960 in av_samples_get_buffer_size (linesize=linesize@entry=0x0, 
    nb_channels=nb_channels@entry=1, nb_samples=1024, 
    sample_fmt=sample_fmt@entry=AV_SAMPLE_FMT_S16, align=align@entry=0)
    at /build/libav-YogfMx/libav-0.8.6/libavutil/samplefmt.c:108
108     /build/libav-YogfMx/libav-0.8.6/libavutil/samplefmt.c: Aucun fichier ou dossier de ce type.
(gdb) bt
[#0](https://code.videolan.org/videolan/vlc/-/issues/0)  0xadc0e960 in av_samples_get_buffer_size (linesize=linesize@entry=0x0, 
    nb_channels=nb_channels@entry=1, nb_samples=1024, 
    sample_fmt=sample_fmt@entry=AV_SAMPLE_FMT_S16, align=align@entry=0)
    at /build/libav-YogfMx/libav-0.8.6/libavutil/samplefmt.c:108
[#1](https://code.videolan.org/videolan/vlc/-/issues/1)  0xae0fe7d5 in avcodec_fill_audio_frame (frame=0xb6f343a0, nb_channels=1, 
    sample_fmt=sample_fmt@entry=AV_SAMPLE_FMT_S16, buf=0xb6f2a540 "", 
    buf_size=2048, align=align@entry=0)
    at /build/libav-YogfMx/libav-0.8.6/libavcodec/utils.c:259
[#2](https://code.videolan.org/videolan/vlc/-/issues/2)  0xaae4848d in EncodeAudio (p_enc=0xb6f004d8, p_aout_buf=0xb6f2a4e8)
    at ../../../modules/codec/avcodec/encoder.c:1240
[#3](https://code.videolan.org/videolan/vlc/-/issues/3)  0xabc778a5 in transcode_audio_process (p_stream=p_stream@entry=0x80f6058, 
    id=id@entry=0xb6f224b0, in=0x0, in@entry=0x82337b0, 
    out=out@entry=0xabaf924c)
    at ../../../modules/stream_out/transcode/audio.c:373
[#4](https://code.videolan.org/videolan/vlc/-/issues/4)  0xabc73b20 in Send (p_stream=0x80f6058, id=0xb6f224b0, p_buffer=0x82337b0)
    at ../../../modules/stream_out/transcode/transcode.c:657
[#5](https://code.videolan.org/videolan/vlc/-/issues/5)  0xb7d89f9d in sout_InputSendBuffer (p_input=0xb6ff7730, 
    p_buffer=p_buffer@entry=0x82337b0)
    at ../../src/stream_output/stream_output.c:233
[#6](https://code.videolan.org/videolan/vlc/-/issues/6)  0xb7d1825f in DecoderPlaySout (p_sout_block=0x82337b0, p_dec=0x8103228)
    at ../../src/input/decoder.c:1672
[#7](https://code.videolan.org/videolan/vlc/-/issues/7)  DecoderProcessSout (p_block=0x0, p_dec=0x8103228)
    at ../../src/input/decoder.c:1794
[#8](https://code.videolan.org/videolan/vlc/-/issues/8)  DecoderProcess (p_dec=p_dec@entry=0x8103228, 
    p_block=p_block@entry=0x82337b0) at ../../src/input/decoder.c:1995
[#9](https://code.videolan.org/videolan/vlc/-/issues/9)  0xb7d18d72 in DecoderThread (p_data=0x8103228)
    at ../../src/input/decoder.c:939
[#10](https://code.videolan.org/videolan/vlc/-/issues/10) 0xb7f92cf1 in start_thread (arg=0xabaf9b40) at pthread_create.c:311
[#11](https://code.videolan.org/videolan/vlc/-/issues/11) 0xb7ec5f4e in clone () at ../sysdeps/unix/sysv/linux/i386/clone.S:131

(Not sure why the native µ-law encoder is not used by the way.)

added Component::Stream output: Encoders Severity::normal Type::bug Version::master git + 1 deleted label

changed milestone to %Bugs paradize

(Answering myself: the native encoder is not used because of "ulaw" instead of "mlaw".)

Note that VLC 2.0.6 works fine using the same libavcodec, so this must be a VLC regression. Most probably in the libavcodec audio encoder component (which changed a lot).

Bisection results:

There are only 'skip'ped commits left to test.
The first bad commit could be any of:
99ba52e3d2fe94122d9c08734975d99d630f409d
f41ea01243bcdba5a92e02b3693895fa88d8d701
We cannot bisect more!

So this one has the bug:

commit f41ea01243bcdba5a92e02b3693895fa88d8d701
Author: Ilkka Ollakka <ileoo@videolan.org>
Date:   Wed Oct 24 22:47:22 2012 +0300

    avcodec: use av_freep in encode_audio2 case too

And that one fails to compile:

commit 99ba52e3d2fe94122d9c08734975d99d630f409d
Author: Ilkka Ollakka <ileoo@videolan.org>
Date:   Wed Oct 24 22:34:16 2012 +0300

    avcodec: flush buffer and use encode_audio2() on audio
    
    Take2 as now we have new enough libavcodec

changed milestone to %2.1.x maintenance bugs

added Status::fixed label

closed

commit 3fd6a569 Author: Tristan Matthews le.businessman@gmail.com Date: Fri May 3 08:28:48 2013 -0400

avcodec: avoid division by zero

Setting align to 0 to get default behaviour only works as of
libavutil 51.27.2 (libav) and 51.46.100 (ffmpeg)
See libav commit 0109a09dc3850eb5dbff84a7bb50eb252a5a8f22
Fixes [#8508](https://code.videolan.org/videolan/vlc/-/issues/8508).

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

Original author: le.businessman@gmail.com

mentioned in issue #8539 (closed)