[FFmpeg-user] Input 5.1 DTS, output 2.0 MP3: Atrocious Quality

[Andy Furniss]

John L wrote:
>>
>> Please test the following:
>> $ ffmpeg -i inter.dts -rematrix_maxval 1.0 -ac 2 out.ac3
>> $ ffmpeg -i inter.dts -rematrix_maxval 1.0 -ac 2 out.mp3
>> $ ffmpeg -i inter.dts -rematrix_maxval 1.0 -ac 2 -acodec pcm_f32le out.wav
>
> I ran all three as requested, including '-loglevel debug'. All three resulting files resulted in poor quality audio as before. the filtergraph output does show something different however, but the resulting audio is still terrible and indistinguishable from before.

That's strange, it seems to do the correct thing for me (only tested 
last one).
I notice typical of "loud movie" dts the master sample is quite extreme 
to start with (and clipped a bit by studio I think).

But ignoring that the downmix with -rematrix_maxval 1.0 is the same for 
me as using a signed wav.

"Looking" with sox

ffmpeg -i inter.dts -rematrix_maxval 1.0 -ac 2 -acodec pcm_f32le outf-1.wav

sox outf-1.wav -n stats
sox WARN wav: wave header missing FmtExt chunk
              Overall     Left      Right
DC offset  -0.000397 -0.000397 -0.000138
Min level  -0.986728 -0.977729 -0.986728
Max level   0.988566  0.974450  0.988566
Pk lev dB      -0.10     -0.20     -0.10
RMS lev dB    -11.54    -11.47    -11.60
RMS Pk dB      -4.73     -4.73     -4.97
RMS Tr dB     -36.11    -36.08    -36.11
Crest factor       -      3.66      3.76
Flat factor     0.00      0.00      0.00
Pk count           2         2         2
Bit-depth      32/32     32/32     32/32
Num samples    1.44M
Length s      29.995
Scale max   1.000000
Window s       0.050

Without -rematrix_maxval 1.0

sox outf-0.wav -n stats
sox WARN wav: wave header missing FmtExt chunk
              Overall     Left      Right
DC offset  -0.005071 -0.005071 -0.002057
Min level  -1.000000 -1.000000 -1.000000
Max level   1.000000  1.000000  1.000000
Pk lev dB       0.00      0.00      0.00
RMS lev dB     -5.62     -5.61     -5.63
RMS Pk dB      -0.79     -0.79     -1.03
RMS Tr dB     -28.46    -28.42    -28.46
Crest factor       -      1.91      1.91
Flat factor    45.34     46.05     44.52
Pk count        222k      228k      216k
Bit-depth      32/32     32/32     32/32
Num samples    1.44M
Length s      29.995
Scale max   1.000000
Window s       0.050
sox WARN sox: `outf-0.wav' input clipped 443634 samples