vpx: misleading error report on 2nd pass

[Christian Ebert]

Summary of the bug:
webm (libvpx) 1st pass does not produce video output. ffmpeg warns (with misleading hints to correct parameters) that output is empty (if no audio is encoded). At 2nd pass an IO Error is reported. It's not fatal, but at least the latter should not be shown at error level. Because it is not an error; or is it?

How to reproduce:

$ ffmpeg -i test.mov -an -pass 1 test.webm
ffmpeg version N-69503-g6a0cd52 Copyright (c) 2000-2015 the FFmpeg developers
  built with Apple LLVM version 6.0 (clang-600.0.56) (based on LLVM 3.5svn)
  configuration: --enable-gpl --enable-version3 --enable-nonfree --disable-ffserver --enable-shared --enable-openssl --enable-libspeex --enable-libfdk-aac --enable-libx265 --enable-libx264 --enable-libxvid --enable-libfaac --enable-libmp3lame --enable-libtheora --enable-libvorbis --enable-libvpx --enable-libvidstab --extra-cflags=-I/sw/include --extra-libs=-L/sw/lib
  libavutil      54. 18.100 / 54. 18.100
  libavcodec     56. 21.102 / 56. 21.102
  libavformat    56. 19.100 / 56. 19.100
  libavdevice    56.  4.100 / 56.  4.100
  libavfilter     5.  9.103 /  5.  9.103
  libswscale      3.  1.101 /  3.  1.101
  libswresample   1.  1.100 /  1.  1.100
  libpostproc    53.  3.100 / 53.  3.100
Guessed Channel Layout for  Input Stream #0.1 : mono
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'test.mov':
  Metadata:
    creation_time   : 1995-10-08 17:44:18
  Duration: 00:00:35.00, start: 0.000000, bitrate: 1385 kb/s
    Stream #0:0(eng): Video: cinepak (cvid / 0x64697663), rgb24, 320x240, 1206 kb/s, 15 fps, 15 tbr, 600 tbn, 600 tbc (default)
    Metadata:
      creation_time   : 1995-10-08 17:44:18
      handler_name    : Apple Alias Data Handler
      encoder         : Cinepak
    Stream #0:1(eng): Audio: pcm_u8 (raw  / 0x20776172), 22254 Hz, 1 channels, u8, 178 kb/s (default)
    Metadata:
      creation_time   : 1995-10-08 17:44:18
      handler_name    : Apple Alias Data Handler
[libvpx @ 0x7fb3bb853200] v1.3.0-5410-g4ed539f
Output #0, webm, to 'test.webm':
  Metadata:
    encoder         : Lavf56.19.100
    Stream #0:0(eng): Video: vp8 (libvpx), yuv420p, 320x240, q=-1--1, pass 1, 200 kb/s, 15 fps, 1k tbn, 15 tbc (default)
    Metadata:
      creation_time   : 1995-10-08 17:44:18
      handler_name    : Apple Alias Data Handler
      encoder         : Lavc56.21.102 libvpx
Stream mapping:
  Stream #0:0 -> #0:0 (cinepak (native) -> vp8 (libvpx))
Press [q] to stop, [?] for help
frame=  525 fps=0.0 q=0.0 Lsize=       0kB time=00:00:00.00 bitrate=N/A
video:0kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown
Output file is empty, nothing was encoded (check -ss / -t / -frames parameters if used)
$ ffmpeg -y -i test.mov -an -pass 2 test.webm
ffmpeg version N-69503-g6a0cd52 Copyright (c) 2000-2015 the FFmpeg developers
  built with Apple LLVM version 6.0 (clang-600.0.56) (based on LLVM 3.5svn)
  configuration: --enable-gpl --enable-version3 --enable-nonfree --disable-ffserver --enable-shared --enable-openssl --enable-libspeex --enable-libfdk-aac --enable-libx265 --enable-libx264 --enable-libxvid --enable-libfaac --enable-libmp3lame --enable-libtheora --enable-libvorbis --enable-libvpx --enable-libvidstab --extra-cflags=-I/sw/include --extra-libs=-L/sw/lib
  libavutil      54. 18.100 / 54. 18.100
  libavcodec     56. 21.102 / 56. 21.102
  libavformat    56. 19.100 / 56. 19.100
  libavdevice    56.  4.100 / 56.  4.100
  libavfilter     5.  9.103 /  5.  9.103
  libswscale      3.  1.101 /  3.  1.101
  libswresample   1.  1.100 /  1.  1.100
  libpostproc    53.  3.100 / 53.  3.100
Guessed Channel Layout for  Input Stream #0.1 : mono
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'test.mov':
  Metadata:
    creation_time   : 1995-10-08 17:44:18
  Duration: 00:00:35.00, start: 0.000000, bitrate: 1385 kb/s
    Stream #0:0(eng): Video: cinepak (cvid / 0x64697663), rgb24, 320x240, 1206 kb/s, 15 fps, 15 tbr, 600 tbn, 600 tbc (default)
    Metadata:
      creation_time   : 1995-10-08 17:44:18
      handler_name    : Apple Alias Data Handler
      encoder         : Cinepak
    Stream #0:1(eng): Audio: pcm_u8 (raw  / 0x20776172), 22254 Hz, 1 channels, u8, 178 kb/s (default)
    Metadata:
      creation_time   : 1995-10-08 17:44:18
      handler_name    : Apple Alias Data Handler
IO error: Undefined error: 0
[libvpx @ 0x7f8ba3053200] v1.3.0-5410-g4ed539f
Output #0, webm, to 'test.webm':
  Metadata:
    encoder         : Lavf56.19.100
    Stream #0:0(eng): Video: vp8 (libvpx), yuv420p, 320x240, q=-1--1, pass 2, 200 kb/s, 15 fps, 1k tbn, 15 tbc (default)
    Metadata:
      creation_time   : 1995-10-08 17:44:18
      handler_name    : Apple Alias Data Handler
      encoder         : Lavc56.21.102 libvpx
Stream mapping:
  Stream #0:0 -> #0:0 (cinepak (native) -> vp8 (libvpx))
Press [q] to stop, [?] for help
frame=  525 fps= 76 q=0.0 Lsize=     859kB time=00:00:35.00 bitrate= 201.1kbits/s
video:855kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.495231%

[Michael Niedermayer]

First part fixed in 4fe38441b0fc2d06dcc98247afb9b029d07a1305
Second part not reproduceable, if it still happens try to update libvpx if that doesnt help please reopen the ticket and provide a input file with which it can be reproduced

[Christian Ebert]

Replying to michael:

First part fixed in 4fe38441b0fc2d06dcc98247afb9b029d07a1305
Second part not reproduceable, if it still happens try to update libvpx if that doesnt help please reopen the ticket and provide a input file with which it can be reproduced

Confirming fix. The second part must have been resolved in some previous version.

Thanks.