[FFmpeg-devel] [PATCH] avcodec: Allow user applications to provide non padded input buffers

[Michael Niedermayer]

This can be extended easily to skip the buffer growing for codecs which do
not need it.

The added field or a equivalent change is needed as the AVBuffer
size might not match the actually allocated and saftely accessable
memory

Signed-off-by: Michael Niedermayer <michaelni at gmx.at>
---
 libavcodec/avcodec.h |   16 ++++++++++++++++
 libavcodec/utils.c   |   19 ++++++++++++++++++-
 2 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/libavcodec/avcodec.h b/libavcodec/avcodec.h
index 99467bb..ed0bee0 100644
--- a/libavcodec/avcodec.h
+++ b/libavcodec/avcodec.h
@@ -3128,6 +3128,18 @@ typedef struct AVCodecContext {
      * - decoding: set by user through AVOPtions (NO direct access)
      */
     char *codec_whitelist;
+
+    /**
+     * Allocated input size
+     * If this is 0 then it is assumed the user allocated size + FF_INPUT_BUFFER_PADDING_SIZE.
+     * Note, many decoders need the padding and will copy/reallocate the buffer
+     * if insufficient padding is provided.
+     * Currently only supported for video.
+     * This also requires the
+     * - encoding: unused
+     * - decoding: set by user, user must access through av_codec_set_allocated_input_size() (NO direct access)
+     */
+    int allocated_input_size;
 } AVCodecContext;
 
 AVRational av_codec_get_pkt_timebase         (const AVCodecContext *avctx);
@@ -3145,6 +3157,9 @@ void av_codec_set_seek_preroll(AVCodecContext *avctx, int val);
 uint16_t *av_codec_get_chroma_intra_matrix(const AVCodecContext *avctx);
 void av_codec_set_chroma_intra_matrix(AVCodecContext *avctx, uint16_t *val);
 
+int av_codec_get_allocated_input_size(const AVCodecContext *avctx);
+void av_codec_set_allocated_input_size(AVCodecContext *avctx, int val);
+
 /**
  * AVProfile.
  */
@@ -4131,6 +4146,7 @@ int avcodec_decode_audio4(AVCodecContext *avctx, AVFrame *frame,
  * @warning The input buffer must be FF_INPUT_BUFFER_PADDING_SIZE larger than
  * the actual read bytes because some optimized bitstream readers read 32 or 64
  * bits at once and could read over the end.
+ * Also @see allocated_input_size.
  *
  * @warning The end of the input buffer buf should be set to 0 to ensure that
  * no overreading happens for damaged MPEG streams.
diff --git a/libavcodec/utils.c b/libavcodec/utils.c
index 1ec5cae..e835b83 100644
--- a/libavcodec/utils.c
+++ b/libavcodec/utils.c
@@ -1274,6 +1274,7 @@ MAKE_ACCESSORS(AVCodecContext, codec, const AVCodecDescriptor *, codec_descripto
 MAKE_ACCESSORS(AVCodecContext, codec, int, lowres)
 MAKE_ACCESSORS(AVCodecContext, codec, int, seek_preroll)
 MAKE_ACCESSORS(AVCodecContext, codec, uint16_t*, chroma_intra_matrix)
+MAKE_ACCESSORS(AVCodecContext, codec, int, allocated_input_size)
 
 int av_codec_get_max_lowres(const AVCodec *codec)
 {
@@ -2333,6 +2334,9 @@ int attribute_align_arg avcodec_decode_video2(AVCodecContext *avctx, AVFrame *pi
     int ret;
     // copy to ensure we do not change avpkt
     AVPacket tmp = *avpkt;
+    int did_split = 0;
+    int needs_copy = avctx->allocated_input_size && avpkt->size &&
+                     avctx->allocated_input_size - avpkt->size < FF_INPUT_BUFFER_PADDING_SIZE;
 
     if (!avctx->codec)
         return AVERROR(EINVAL);
@@ -2347,8 +2351,19 @@ int attribute_align_arg avcodec_decode_video2(AVCodecContext *avctx, AVFrame *pi
 
     av_frame_unref(picture);
 
+    if (needs_copy) {
+        memset(&tmp, 0, sizeof(tmp));
+        if ((ret = av_packet_ref(&tmp, avpkt)) < 0) {
+            needs_copy = 0;
+            goto fail;
+        }
+        if ((ret = av_grow_packet(&tmp, FF_INPUT_BUFFER_PADDING_SIZE)) < 0)
+            goto fail;
+        tmp.size -= FF_INPUT_BUFFER_PADDING_SIZE;
+    }
+
     if ((avctx->codec->capabilities & CODEC_CAP_DELAY) || avpkt->size || (avctx->active_thread_type & FF_THREAD_FRAME)) {
-        int did_split = av_packet_split_side_data(&tmp);
+        did_split = av_packet_split_side_data(&tmp);
         ret = apply_param_change(avctx, &tmp);
         if (ret < 0) {
             av_log(avctx, AV_LOG_ERROR, "Error applying parameter changes.\n");
@@ -2388,6 +2403,8 @@ fail:
             if(ret == tmp.size)
                 ret = avpkt->size;
         }
+        if (needs_copy)
+            av_packet_unref(&tmp);
 
         if (*got_picture_ptr) {
             if (!avctx->refcounted_frames) {
-- 
1.7.9.5