[FFmpeg-user] ac3 to mp3 converting bug

[Ingo Brückl]

Clément Boesch wrote on Wed, 4 Jul 2012 10:13:15 +0200:

>> > Le sextidi 16 messidor, an CCXX, Ingo Brückl a écrit :
>> >> Sure. What information would you need?
>>
>> > All you can give on how to reproduce the problem.
>>
>> I'm afraid there is hardly more I can tell than I already did in my
>> postings

> What do you use for playback for instance (ffplay, MPlayer?)

MPlayer, but that shouldn't make a difference, because the mp3 output file
only consists of large 0x55 blocks as stated earlier. This hardly is any
converted audio data. (Don't know if it's typical for silence though.)

> Also, since you mentioned the *static* libmp3lame, is the issue
> reproducible with a shared version?

Oops, a shared libmp3lame segfaults!

  Program received signal SIGSEGV, Segmentation fault.
  0xb7ed87cd in count_bits () from /usr/lib/libmp3lame.so.0

This happens with non-2.0 ac3 like monsters_inc_5.1_448.ac3, but not with 2.0
ac3 like monsters_inc_2.0_192.ac3, for example.

Configuring lame with --enable-debug=alot leads to:

  Program received signal SIGFPE, Arithmetic exception.
  0xb7ec4f64 in lame_encode_buffer_template (gfp=<optimized out>,
      buffer_l=0x8f26520, buffer_r=0x8f26522, nsamples=1152,
      mp3buf=0x8f2794c "", mp3buf_size=10792, pcm_type=pcm_short_type, aa=2,
      norm=1) at lame.c:1882
  1882                    lame_copy_inbuffer(gfc, buffer_l, buffer_r, nsamples, pcm_type, aa, norm);

and a backtrace prints:

  #0  0xb7ec4f64 in lame_encode_buffer_template (gfp=<optimized out>,
      buffer_l=0x8f26520, buffer_r=0x8f26522, nsamples=1152,
      mp3buf=0x8f2794c "", mp3buf_size=10792, pcm_type=pcm_short_type, aa=2,
      norm=1) at lame.c:1882
  #1  0xb7ec52e6 in lame_encode_buffer_interleaved (gfp=0x8f7df88,
      pcm=0x8f26520, nsamples=1152, mp3buf=0x8f2794c "", mp3buf_size=10792)
      at lame.c:1995
  #2  0x0846a007 in encode_frame_int16 (nb_samples=<optimized out>,
      samples=<optimized out>, s=<optimized out>) at libavcodec/libmp3lame.c:165
  #3  mp3lame_encode_frame (avctx=0x8f78560, avpkt=0xbffff01c, frame=0x8f26300,
      got_packet_ptr=0xbffff160) at libavcodec/libmp3lame.c:209
  #4  0x085aad20 in avcodec_encode_audio2 (avctx=0x8f78560, avpkt=0xbffff01c,
      frame=0x8f26300, got_packet_ptr=0x8fccd28) at libavcodec/utils.c:1147
  #5  0x08094b92 in do_audio_out (frame=<optimized out>, ost=<optimized out>,
      s=<optimized out>) at ffmpeg.c:1583
  #6  poll_filters () at ffmpeg.c:1990
  #7  0x08098143 in transcode () at ffmpeg.c:3671
  #8  main (argc=-487877, argv=0x0) at ffmpeg.c:5962

> Is that only reproducible with AC3 --> MP3? Can you try with, let's say
> flac or a libvorbis?

I've neither installed flac nor vorbis libraries on my PC, but could do so
if that'd help (please tell me). On the other side, we've already established
that converting to wav or mp2 works fine, so it seems to be related to mp3
output only.

> Monster's Inc samples, as well as Broadway start with silence anyway, what
> about TomorrowNeverDies-2.1-48khz-192kbit.ac3?

A completely mute file as well and, in addition, some errors (with static
lame, shared lame crashing):

  [ac3 @ 0x9ab2620] frame sync error
  Error while decoding stream #0:0: Operation not permitted
  [ac3 @ 0x9ab2620] frame CRC mismatch

> Like the others I can't reproduce the issue as well. It's not about not
> believing the issue does not exist and doesn't come from this commit,

I'm wondering what this commit changes in process with otherwise identical
libraries.

Ingo