On 21/03/2024 10:40, Marton Balint wrote:
On Thu, 21 Mar 2024, Tobias Rapp wrote:
On 19/03/2024 20:14, Marton Balint wrote:
On Tue, 19 Mar 2024, Michael Niedermayer wrote:
On Sun, Mar 17, 2024 at 08:57:29PM +0100, Marton Balint wrote:
- Only parse the defined masks in dwChannelMask, unless
strict_std_compliance
is less than normal. This matches with the behaviour of the wav
muxer.
- Ignore additional bits in dwChannelMasks as the MS documentation
suggests [1]
- Assume UNKNOWN channels for missing bits as the MS documentation
suggests [1]
[1]
https://learn.microsoft.com/en-us/previous-versions/windows/hardware/design/dn653308(v=vs.85)#details-about-dwchannelmask
Signed-off-by: Marton Balint <c...@passwd.hu>
---
libavformat/riffdec.c | 28 +++++++++++++++++++++++++---
1 file changed, 25 insertions(+), 3 deletions(-)
breaks:
./ffmpeg -i ~/tickets/2859/5.1plusdownmix.wav -ac 2 -t 100 -bitexact
-c:a aac -y /tmp/2859-frenchspeack-nolibfaac.mp4
After the patch this is file will need -strict unofficial to work,
since
the downmix channels are not officially recognized in the
dwChannelMask.
I think downmix channels are part of the RF64 specification, see EBU
Tech 3306 section 3.1:
"""
3.1 Enhancement for a PCM stereo down mix
No PCM stereo signal is included in the basic Wave Format Extensible.
To include a stereo channel the following is added:
#define SPEAKER_STEREO_LEFT 0x20000000
#define SPEAKER_STEREO_RIGHT 0x40000000
"""
I was reluctant to add these, because the recommendation which
superseded this, ITU BS.2088 does not mention these masks.
Nevertheless, you are right, these should be recognized to support
historical RF64 files. Or we should not even make the distinction of
RF64?
WAV files smaller than 2/4GiB could start with the usual "RIFF" bytes
but still contain these mask bits. From a quick glance at ITU BS.2088 it
seems it could use the "chna" chunk to achieve a mapping like "5.1 +
downmix".
Having said that, I have not stumbled over "X plus downmix" WAVE files
in production yet. So no strong opinion from my side on whether this
should work without "-strict unofficial", or not.
Regards, Tobias
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