Matrox m705 (RGBA) coded video has alpha problem on playing

General
1

Hello everyone,

Casparcg don’t play alpha channel for matrox m705 coded avi files. If I convert the m705 coded file to lagarith coded avi file, the file playing perfectly with alpha channel.
I thing ffmpeg doesn’t support m705 codec also vfw codecs chunk.
I have install m705 vfw codec the server. Is there a way to using vfw decoders?
Also is there an other video producer that can play vfw coded video files?

Any idea?

Thanks in advance

2

What version of CasparCG?

We are using ffmpeg for all video decoding, if a particular codec isn’t working correctly then it will most likely either be that ffmpeg doesn’t support it or has a bug (it looks like m705 might be supported), or perhaps the version of ffmpeg we use is too old.

3

Hi,
CasparCG version: v2.3.3-lts-stable.

Then, when ffmpeg decodes the m705 coded video, it decodes it as RGB, not RGBA. I think that’s the problem and the problem with ffmpeg’s decoding.

In this case, do I need to write an m705 producer to decode the m705 video with the alpha channel?

Best regards,

4

Is transcoding not an option?

5

Transcoding is not an option because all contents are shared other system.

6

Perhaps it would be worth trying the master/2.4 builds? They have an updated ffmpeg, so it is possible they will behave differently.

The solution depends on why it is treating it as RGB instead of RGBA.
It could be any of:

  • ffmpeg doesn’t support decoding the alpha
  • ffmpeg needs to be told to decode the alpha, which we aren’t doing
  • our ffmpeg producer is discarding the alpha

But I don’t think the solution is to write a new producer, we have a single ffmpeg producer currently which handles all video files. Having a separate one for this codec will require reimplementing the decoding from scratch, and will need some thought on how to direct play commands to the correct producer.
For your use case this may be fine, but I wont accept a PR with a new producer for this.

Instead, it should be possible to fix this within the current ffmpeg producer we have. Maybe it will require patching ffmpeg, or maybe it is something that can be fixed in the producer. I can’t say which it will be without knowing more on why CasparCG isnt playing the alpha