Opened 5 years ago

Last modified 3 years ago

#3455 new defect

aresample=matrix_encoding=dplii doesn't downmix backleft and center correctly

Reported by: Peter Owned by:
Priority: normal Component: swresample
Version: git-master Keywords: dplii
Cc: Blocked By:
Blocking: Reproduced by developer: no
Analyzed by developer: no

Description

Summary of the bug: DPLII files have too-loud right channel.
Seems to be some problem with the interaction of back left and center channel
How to reproduce:

ffmpeg -i surround_blbrc.wav -af "aresample=matrix_encoding=dplii" -ac 2 dplii_blbrc.wav
ffmpeg version git-2014-03-09-8dfd0e6
built on Mar  9 2014 22:53:26 with gcc 4.8.2 (Gentoo 4.8.2 p1.3r1, pie-0.5.8r1)

You can see the problem easiest by crafting a 5.1 surround wave file with empty channels except the center channel with noise and the two back channels, first half of the back left with noise and the second half of the back right with noise. However, all surround files that use the bl and center channels at the same time will be too loud in the resulting file's right channel.

Can provide example files if you like.

Attachments (2)

surround_blbrc.wav (568.2 KB) - added by Peter 5 years ago.
Input sample for #3455
dplii_blbrc.wav (189.5 KB) - added by Peter 5 years ago.
Output sample for #3455

Download all attachments as: .zip

Change History (9)

comment:1 Changed 5 years ago by cehoyos

  • Component changed from ffmpeg to swresample
  • Keywords aresample matrix_encoding dplii removed

Please provide your failing command line together with the complete, uncut console output and please provide a sample.

Changed 5 years ago by Peter

Input sample for #3455

Changed 5 years ago by Peter

Output sample for #3455

comment:2 Changed 5 years ago by Peter

peter@Chip /run/media/peter/FRAPs/LetsPlay $ ~/mplayer/ffmpeg/ffmpeg -i surround_blbrc.wav -af "aresample=matrix_encoding=dplii" -ac 2 dplii_blbrc.wav
ffmpeg version git-2014-03-09-8dfd0e6 Copyright (c) 2000-2014 the FFmpeg developers
  built on Mar  9 2014 22:53:26 with gcc 4.8.2 (Gentoo 4.8.2 p1.3r1, pie-0.5.8r1)
  configuration: --enable-libx264 --enable-gpl
  libavutil      52. 66.101 / 52. 66.101
  libavcodec     55. 52.102 / 55. 52.102
  libavformat    55. 34.100 / 55. 34.100
  libavdevice    55. 11.100 / 55. 11.100
  libavfilter     4.  3.100 /  4.  3.100
  libswscale      2.  5.101 /  2.  5.101
  libswresample   0. 18.100 /  0. 18.100
  libpostproc    52.  3.100 / 52.  3.100
Guessed Channel Layout for  Input Stream #0.0 : 5.1
Input #0, wav, from 'surround_blbrc.wav':
  Duration: 00:00:01.01, bitrate: 4608 kb/s
    Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 48000 Hz, 5.1, s16, 4608 kb/s
File 'dplii_blbrc.wav' already exists. Overwrite ? [y/N] y
Output #0, wav, to 'dplii_blbrc.wav':
  Metadata:
    ISFT            : Lavf55.34.100
    Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 48000 Hz, stereo, s16, 1536 kb/s
Stream mapping:
  Stream #0:0 -> #0:0 (pcm_s16le -> pcm_s16le)
Press [q] to stop, [?] for help
size=     189kB time=00:00:01.01 bitrate=1536.6kbits/s    
video:0kB audio:189kB subtitle:0 data:0 global headers:0kB muxing overhead 0.041252%
Last edited 5 years ago by cehoyos (previous) (diff)

comment:3 Changed 5 years ago by Peter

I can fix this problem by inverting the back-left channel of my source files before letting ffmpeg do its thing - it seems like ffmpeg is subtracting the back left from the center channel rather than adding it which means it is inverting the back-left when it shouldn't or not inverting it when it should.

I'll do some tinkering over the weekend and see if I can't figure out some demonstration to attach.

comment:4 Changed 5 years ago by cehoyos

The sample you uploaded is too short to do any test imo, I tested with a file that you should be able to find with Google:

$ ffmpeg -i Test\ AC3\ v2.0.avi -af "aresample=matrix_encoding=dplii" -ac 2 out.wav
$ ffmpeg -i Test\ AC3\ v2.0.avi -af "aresample=matrix_encoding=dplii" -ac 2 -ab 640k out.ac3
$ ffmpeg -i Test\ AC3\ v2.0.avi -af "aresample=matrix_encoding=dplii" -ac 2 -ab 640k out.eac3

I now set my receiver to "PLII" and played the three files over the digital connection (HDMI): The surround sound sounded as expected (surround sound although I used stereo files). I finally tested the wav file over the analog connection and the stereo signal also played like a surround signal.

Or do I misunderstand the problem?

Last edited 5 years ago by cehoyos (previous) (diff)

comment:6 Changed 3 years ago by cehoyos

See also #4175.

comment:7 Changed 3 years ago by cehoyos

  • Keywords dplii added
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