Feature #6061

Expose and pass information to commands in "MPEG-TS Spawn" from TvH

Added by Bogdan I. about 2 months ago.

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Commands run by "MPEG-TS Spawn" Streaming Profiles could benefit from injecting basic data from Tvheadend.

For example, one could export the profile name, service-id, channel-id etc. by using setenv(), or by doing string replacement.

Setting Environment Variables via setenv() would probably be simpler to implement than string replacement and it's probably safer for the end-user.

For example, diong this in src/spawn.c:

    setenv("THISISNEW", "test", 1);

Will properly set an environment variable called THISISNEW="test".

When creating a streaming profile that uses a bash script with the following contents:

export -p > "/tmp/dump-vars" 
/usr/bin/ffmpeg -nostats -v verbose -i - -c copy -copy_unknown -f mpegts -

You can find the THISISNEW="test" in tmp/dump-vars

Unfortunately my C skills are pretty much non-existent, and my attempts in actually grabbing the info and passing them to spawn_with_passthrough() have failed spectacularly.

What would be the use-case?

As for the motivation for this feature, I'm currently limited to ~2GiB GPU memory on my Tvh machine that runs with a cheap GTX 1050. Due to the current GPU shortage we are facing right now, upgrading to anything with more VRAM doesn't look too possible in the near future...

Loading up a full 1080p/i stream in GPU memory to transcode uses about 400-450MiB VRAM.

Unfortunately, if 2 users are currently watching the same channel/stream, even with the same Streaming Profile, the transcoding operation is done twice, thus using resources twice, needlessly.

In my quest to write a script to tackle this, which would write HLS and then re-read it if the Stream is already transcoding... I realized that I'm kind of limited by not having an actual way of know if a specific stream is already being transcoded.

Ideally I should be able to create a file from my script to check if there's a transcode going on for that specific stream with that specific profile

This could probably be useful for lots of people who are adventurous enough to implement their own transcoding scripts/tools.

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