lavc: Add support for increasing hardware frame pool sizes

AVCodecContext.extra_hw_frames is added to the size of hardware frame
pools created by libavcodec for APIs which require fixed-size pools.
This allows the user to keep references to a greater number of frames
after decode, which may be necessary for some use-cases.

It is also added to the initial_pool_size value returned by
avcodec_get_hw_frames_parameters() if a fixed-size pool is required.

1 files changed, 14 insertions, 0 deletions

diff --git a/libavcodec/avcodec.h b/libavcodec/avcodec.h
index 7eaa0c9277..03a3d5bd6d 100644
--- a/libavcodec/avcodec.h
+++ b/libavcodec/avcodec.h
@@ -2739,6 +2739,20 @@ typedef struct AVCodecContext {
      *             AVCodecContext.get_format callback)
      */
     int hwaccel_flags;
+
+    /**
+     * Video decoding only.  Sets the number of extra hardware frames which
+     * the decoder will allocate for use by the caller.  This must be set
+     * before avcodec_open2() is called.
+     *
+     * Some hardware decoders require all frames that they will use for
+     * output to be defined in advance before decoding starts.  For such
+     * decoders, the hardware frame pool must therefore be of a fixed size.
+     * The extra frames set here are on top of any number that the decoder
+     * needs internally in order to operate normally (for example, frames
+     * used as reference pictures).
+     */
+    int extra_hw_frames;
 } AVCodecContext;
 
 /**