[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.

Signed-off-by: Michael Niedermayer <michaelni at gmx.at>
---
 libavcodec/avcodec.h |    8 +++++++-
 libavcodec/utils.c   |   12 ++++++++++--
 2 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/libavcodec/avcodec.h b/libavcodec/avcodec.h
index 99467bb..ec95194 100644
--- a/libavcodec/avcodec.h
+++ b/libavcodec/avcodec.h
@@ -4128,9 +4128,15 @@ int avcodec_decode_audio4(AVCodecContext *avctx, AVFrame *frame,
  * Some decoders may support multiple frames in a single AVPacket, such
  * decoders would then just decode the first frame.
  *
- * @warning The input buffer must be FF_INPUT_BUFFER_PADDING_SIZE larger than
+ * @warning If you use non AVBuffer based AVPackets, then 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.
+ * If you do use AVBuffer based AVPackets and the allocated space as indicated
+ * by the AVBuffer does not include FF_INPUT_BUFFER_PADDING_SIZE padding then
+ * many decoders will reallocate the buffer.
+ * Most AVPacket as created by the FFmpeg APIs will already include the needed
+ * padding.
  *
  * @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..eaa0431 100644
--- a/libavcodec/utils.c
+++ b/libavcodec/utils.c
@@ -2332,7 +2332,8 @@ int attribute_align_arg avcodec_decode_video2(AVCodecContext *avctx, AVFrame *pi
     AVCodecInternal *avci = avctx->internal;
     int ret;
     // copy to ensure we do not change avpkt
-    AVPacket tmp = *avpkt;
+    AVPacket tmp;
+    int did_split = 0;
 
     if (!avctx->codec)
         return AVERROR(EINVAL);
@@ -2347,8 +2348,15 @@ int attribute_align_arg avcodec_decode_video2(AVCodecContext *avctx, AVFrame *pi
 
     av_frame_unref(picture);
 
+    if (avpkt->buf && avpkt->size && avpkt->buf->size - avpkt->size < FF_INPUT_BUFFER_PADDING_SIZE) {
+        if ((ret = av_grow_packet(avpkt, FF_INPUT_BUFFER_PADDING_SIZE)) < 0)
+            goto fail;
+        tmp.size -= FF_INPUT_BUFFER_PADDING_SIZE;
+    }
+    tmp = *avpkt;
+
     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");
-- 
1.7.9.5