Open eugenesvk opened 2 years ago
We don't have libfdk_aac, please attach a sample file.
Maybe I'm misunderstanding what this layout means, but shouldn't it always be two channels for a stere file there (in both cases the Channel(s) field has the correct value of 2 channel)?
We rely on file metadata, I'll check the metadata in the resulting file. a wrong metadata "C" somewhere would not be a surprise because HE-AAC is basically a mono stream (and handled as mono by decoder supporting AAC but not supporting HE-AAC) with spectral band replication.
Sure, here is a sine2ch5s_wav_AAC-FDK_HEv2_vbr3_ffmpeg.m4a file (though I thought a non-file-based solution would be simpler to replicate)
By the way, HE
(that is, AAC LC SBR
without PS
Parametric Stereo) shows the same L R
as LC
, so it might not be the SBR to blame, but the PS
Now that you mentioned metadata, I've digged a bit into the Debug mode in MediaInfo and there is indeed a difference between
HEv2
channelConfiguration: 1 (0x1) - (4 bits) - Front: C
and HE
(or LC
)
channelConfiguration: 2 (0x2) - (4 bits) - Front: L R
though all 3 files have the same channel count
channelcount (2): 2 (0x0002)
and from PS wiki
An AAC HE v2 bitstream is obtained by downmixing the stereo audio to mono at the encoder along with 2–3 kbit/s of side info (the Parametric Stereo information) in order to describe the spatial intensity stereo generation and ambience regeneration at the decoder.
So you're right, it's indeed one channel with extra info to get back to two channels, and indeed nothing's wrong with MediaInfo Thanks for pointing me to the right direction!
(though I thought a non-file-based solution would be simpler to replicate)
It is good but in that case I was not having the right config. Copy: sine2ch5s_wav_AAC-FDK_HEv2_vbr3_ffmpeg.zip
so it might not be the SBR to blame, but the PS
Oops, I mixed up both. True, I was speaking about Parametric Stereo.
Now that you mentioned metadata,
Yes and no: it is implicit signaling (no info in the descriptor) but it is still all about AAC, so I consider that we should correctly provide the "L R" info as we catch PS (both are linked). I was thinking about an extra metadata in e.g. the MP4, but it is not the case. So this is a coherency issue, I reopen the ticket.
For some reason MediaInfo shows only one channel
C
inChannel layout
for a stere file when it's encoded using theaac_he_v2
profile of theFDK-AAC
encoder, please see the script below where I convert a generated wav with:aac_low
(LC, default) andaac_he_v2
profilesMediaInfo is different for these two files:
aac_low
showsL R
inChannel layout
, while theaac_he_v2
shows only one channelC
thereMaybe I'm misunderstanding what this layout means, but shouldn't it always be two channels for a stere file there (in both cases the
Channel(s)
field has the correct value of2 channel
)?