Re: [FFmpeg-devel] [PATCH 1/3] avcodec/cbs: add a helper to read extradata within packet side data

[James Almer]

On 8/5/2021 12:43 PM, Andreas Rheinhardt wrote:
James Almer:
Using ff_cbs_read() on the raw buffer will not parse it as extradata,
resulting in parsing errors for example when handling ISOBMFF avcC.
This helper works around that.
Signed-off-by: James Almer <jamr...@gmail.com>
---
  libavcodec/cbs.c | 13 +++++++++++++
  libavcodec/cbs.h |  4 ++++
  2 files changed, 17 insertions(+)

diff --git a/libavcodec/cbs.c b/libavcodec/cbs.c
index 8d50ea1432..f6e371ddef 100644
--- a/libavcodec/cbs.c
+++ b/libavcodec/cbs.c
@@ -294,6 +294,19 @@ int ff_cbs_read_packet(CodedBitstreamContext *ctx,
                           pkt->data, pkt->size, 0);
  }
  
+int ff_cbs_read_packet_side_data(CodedBitstreamContext *ctx,
+                                 CodedBitstreamFragment *frag,
+                                 const AVPacket *pkt)
+{
+    size_t side_data_size;
+    const uint8_t *side_data =
+        av_packet_get_side_data(pkt, AV_PKT_DATA_NEW_EXTRADATA,
+                                &side_data_size);
+
+    return cbs_read_data(ctx, frag, NULL,
+                         side_data, side_data_size, 1);
+}
+
  int ff_cbs_read(CodedBitstreamContext *ctx,
                  CodedBitstreamFragment *frag,
                  const uint8_t *data, size_t size)
diff --git a/libavcodec/cbs.h b/libavcodec/cbs.h
index b7acf98347..bd97d163b1 100644
--- a/libavcodec/cbs.h
+++ b/libavcodec/cbs.h
@@ -276,6 +276,10 @@ int ff_cbs_read_extradata_from_codec(CodedBitstreamContext 
*ctx,
                                       CodedBitstreamFragment *frag,
                                       const struct AVCodecContext *avctx);
  
+int ff_cbs_read_packet_side_data(CodedBitstreamContext *ctx,
+                                 CodedBitstreamFragment *frag,
+                                 const AVPacket *pkt);
+
  /**
   * Read the data bitstream from a packet into a fragment, then
   * split into units and decompose.

Despite using this function in both 2 and 3 the callers still have to
check for whether extradata exists in the first place; in patch 3 this
is unavoidable. This makes me wonder whether it might not be better to
expose the header flag in ff_cbs_read().

- Andreas

It's no different than existing callers of ff_cbs_read_extradata and 
ff_cbs_read_extradata_from_codec(), which check for avctx/par->extradata 
before calling either of them.
I personally prefer these helpers as is.
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