lighter 0.13.1

A video stream whose picture gets smaller as it plays now goes on decoding on your Mac's media engine, at its new size, instead of stopping where the size changed.

What went wrong

A stream that shrank stopped at the change. A camera whose resolution is lowered while it streams, or a recording that switches to a smaller picture, sends its new size mid-stream. lighter's decoder reported a larger size as changed, but a smaller one as the old size, because it kept CAPTURE's buffers at the largest size it had seen. Debian's ffmpeg (h264_v4l2m2m), told nothing had changed, read the end of the old picture size as the end of the stream: a 640x360 clip that turned 320x180 gave 90 of its 120 frames, and exit code 0.

Reporting the new size properly brought two more problems to light, both fixed:

• Frames could reach buffers the guest was about to discard. After a size change, a decoder must stop until the guest has set up buffers for the new size. lighter went on, and once a picture shrank, the old, larger buffers were big enough for it, so new frames could go into them and be thrown away with them.
• The guest kernel told ffmpeg the device had failed in the middle of the change. Its video driver reported an error from poll whenever the decoder's output queue was off, which it is while a client switches to new buffers. ffmpeg, polling at that moment, looks through the buffers it has just freed and crashes. In our tests 0.13.0 never reached that moment; the corrected decoder did.

What changed

• After a size change, the decoder reports the stream's new size, smaller or larger, and stops at the end of the old size until the guest has set up for the new one, as the V4L2 standard describes; frames of the new size go only into buffers made for it.
• The guest kernel's video driver reports an error only when neither of the decoder's queues can make progress, as Linux's own decoders do.

ffmpeg decodes a 640x360 stream that turns 320x180, and one that does the reverse, to the same 120 frames, at both sizes, as its software decoder.

Upgrading

brew upgrade lighter
lighter restart

Or lighter update download then lighter upgrade --restart if you installed with the install script.

Also

• Linux remains 6.18.52, with the video driver change (kernel 8a99a707). The data epoch remains 1.