ffmpeg CLI pixel format selection for filtering currently special-cases
MJPEG encoding, where it will restrict the supported list of pixel
formats depending on the value of the -strict option. In order to get
that value it will apply it from the options dict into the encoder
context, which is a highly invasive action even now, and would become a
race once encoding is moved to its own thread.
The ugliness of this code can be much reduced by moving the special
handling of MJPEG into ofilter_bind_ost(), which is called from encoder
init and is thus synchronized with it. There is also no need to write
anything to the encoder context, we can evaluate the option into our
stack variable.
There is also no need to access AVCodec at all during pixel format
selection, as the pixel formats array is already stored in
OutputFilterPriv.
When no frames were passed from a filtergraph to an encoder, but the
filtergraph is configured (i.e. has output parameters), encoder flush
code will use those parameters to initialize the encoder in a last-ditch
effort to produce some useful output.
Rework this process so that it is triggered by the filtergraph, which
now sends a dummy frame with parameters, but no data, to the encoder,
rather than the encoder reaching backwards into the filter.
This approach is more in line with the natural data flow from filters to
encoders and will allow to reduce encoder-filter interactions in
following commits.
This code is tested by fate-adpcm-ima-cunning-trunc-t2-track1, which (as
confirmed by Zane) is supposed to produce empty output.
Make all relevant state per-filtergraph input, rather than per-input
stream. Refactor the code to make it work and avoid leaking memory when
a single subtitle stream is sent to multiple filters.
Set them in ifilter_parameters_from_dec(), similarly to audio/video
streams. This reduces the extent to which sub2video filters need to be
treated specially.
This queue should be associated with a specific filtergraph input - if
a subtitle stream is sent to multiple filters then each should have its
own queue.
This code is a sub2video analogue of ifilter_send_frame(), so it
properly belongs to the filtering code.
Note that using sub2video with more than one target for a given input
subtitle stream is currently broken and this commit does not change
that. It will be addressed in following commits.
When the filtergraph has no inputs, it can be configured immediately
when all its outputs are bound to output streams. This will simplify
treating some corner cases.
This way the list of filtergraph inputs/outputs is always known after
FilterGraph creation. This will allow treating simple and complex
filtergraphs in a more uniform manner.
