This gets rid of the reliance on the decode only flag that is still
set on input buffers to the decoder if they are less than the start
time.
We still need to set and check the decode-only flag in SimpleDecoder
to ensure compatbility with custom decoders that use the flag while
it's not fully removed.
PiperOrigin-RevId: 570736692
MP4 edit lists sometimes ask to start playback between two samples.
If this happens, we currently change the timestamp of the first
sample to zero to trim it (e.g. to display the first frame for a
slightly shorter period of time). However, we can't do this to audio
samples are they have an inherent duration and trimming them this
way is not possible.
#minor-release
PiperOrigin-RevId: 543420218
