lavc: Use hardware config information in ff_get_format()

This removes the dependency that hardware pixel formats previously had on
AVHWAccel instances, meaning only those which actually do something need
exist after this patch.

Also updates avcodec_default_get_format() to be able to choose hardware
formats if either a matching device has been supplied or no additional
external configuration is required, and avcodec_get_hw_frames_parameters()
to use the hardware config rather than searching the old hwaccel list.

The FF_CODEC_CAP_HWACCEL_REQUIRE_CLASS mechanism is deleted because it
no longer does anything (the codec already contains the pointers to the
matching hwaccels).

libavcodec/avcodec.h

@@ -3652,13 +3652,6 @@ typedef struct AVHWAccel {
      * that avctx->hwaccel_priv_data is invalid.
      */
     int (*frame_params)(AVCodecContext *avctx, AVBufferRef *hw_frames_ctx);
-
-    /**
-     * Some hwaccels are ambiguous if only the id and pix_fmt fields are used.
-     * If non-NULL, the associated AVCodec must have
-     * FF_CODEC_CAP_HWACCEL_REQUIRE_CLASS set.
-     */
-    const AVClass *decoder_class;
 } AVHWAccel;
 
 /**

libavcodec/cuviddec.c

@@ -1120,7 +1120,6 @@ static const AVCodecHWConfigInternal *cuvid_hw_configs[] = {
         .type           = AVMEDIA_TYPE_VIDEO, \
         .id             = AV_CODEC_ID_##X, \
         .pix_fmt        = AV_PIX_FMT_CUDA, \
-        .decoder_class  = &x##_cuvid_class, \
     }; \
     AVCodec ff_##x##_cuvid_decoder = { \
         .name           = #x "_cuvid", \
@@ -1135,7 +1134,6 @@ static const AVCodecHWConfigInternal *cuvid_hw_configs[] = {
         .receive_frame  = cuvid_output_frame, \
         .flush          = cuvid_flush, \
         .capabilities   = AV_CODEC_CAP_DELAY | AV_CODEC_CAP_AVOID_PROBING, \
-        .caps_internal  = FF_CODEC_CAP_HWACCEL_REQUIRE_CLASS, \
         .pix_fmts       = (const enum AVPixelFormat[]){ AV_PIX_FMT_CUDA, \
                                                         AV_PIX_FMT_NV12, \
                                                         AV_PIX_FMT_P010, \

libavcodec/internal.h

@@ -69,11 +69,6 @@
  */
 #define FF_CODEC_CAP_SLICE_THREAD_HAS_MF    (1 << 5)
 
-/**
- * Allow only AVHWAccels which have a matching decoder_class field.
- */
-#define FF_CODEC_CAP_HWACCEL_REQUIRE_CLASS  (1 << 6)
-
 #ifdef TRACE
 #   define ff_tlog(ctx, ...) av_log(ctx, AV_LOG_TRACE, __VA_ARGS__)
 #else
@@ -377,6 +372,12 @@ int ff_side_data_update_matrix_encoding(AVFrame *frame,
  * Select the (possibly hardware accelerated) pixel format.
  * This is a wrapper around AVCodecContext.get_format() and should be used
  * instead of calling get_format() directly.
+ *
+ * The list of pixel formats must contain at least one valid entry, and is
+ * terminated with AV_PIX_FMT_NONE.  If it is possible to decode to software,
+ * the last entry in the list must be the most accurate software format.
+ * If it is not possible to decode to software, AVCodecContext.sw_pix_fmt
+ * must be set before calling this function.
  */
 int ff_get_format(AVCodecContext *avctx, const enum AVPixelFormat *fmt);