Definitions:

A Decoder class decodes a frame

A DecoderThread class uses a Decoder and takes care of queueing the frames, mutexes, synchronization, etc.

Details

Decoder subclassing as currently practised:

Decoder (virtual) BasicFrame input_frame output_frame: defined in subclasses as type depends on decoder flush() virtual Frame *output() = 0 : returns a reference to output_frame virtual bool pull() = 0 # decode! isOK() # is the decoder still working?

AVDecoder : Decoder (virtual) Audio or video decoding using libav AVCodecID, AVPAcket, AVCodecContext, etc. libav paraphernalia initiated at the ctor

VideoDecoder : AVDecoder Video decoding using libav AVBitmapFrame out_frame implements Frame *output() that returns out_frame implements pull(): AVPacket's etc. filled with in_frame, results into out_frame

AVHwDecoder : Decoder (virtual) Audio or video decoding using libav with hardware acceleration Takes as an input, the libav AVHWDeviceType Like AVDecoder, but creates also AVBufferRef hardware context: AVCodecID, AVPAcket, AVCodecContext, AVBufferRef etc. libav paraphernalia initiated at the ctor NOTE: most of the ctor code copy-pasted from AVDecoder

HWVideoDecoder : AVHwDecoder Hw accelerated video decoding using libav Takes as an input, the libav AVHWDeviceType Identical (a copy-paste) to VideoDecoder

NOTE: if all the contexes, etc. were not created at ctor but in another method (say, "init"), we could create saner subclass structure. --> then the DecoderThread::chooseVideoDecoder should call that "init" method just after "new".

DecoderThread classes use the Decoder classes and run the queues, semaphores, etc.

DecoderThread

virtual Decoder* chooseVideoDecoder(AVCodecID codec_id);
    returns a Decoder instance or NULL of none avail for the codec_id

virtual Decoder* fallbackVideoDecoder(AVCodecID codec_id);
    returns a second option Decoder instance or NULL of none avail for the codec_id

run
    - DecoderThread receives SetupFrame(s) and BasicFrames(s)
    - On receiving a SetupFrame, it tries to get a new Decoder by
      calling chooseVideoDecoder
    - It regularly calls Decoder::isOk() -> if that returns false,
      it calls fallbackVideoDecoder

VideoDecoder::pull logic:

current_pixel_format assumed initially AV_PIX_FMT_YUV420P

Then in method pull:

if AV_PIX_FMT_YUV420P --> decode directly to out_frame.av_frame (all good!)

if not, decode to aux_av_frame

--> both refer to av_ref_frame reference pointer

After the fact, check the frame's (av_ref_frame) pix fmt. If it has changed, set up infra to sws scale the pix fmt into AV_PIX_FMT_YUV420P