[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 <jamrial at 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.