[FFmpeg-devel] [PATCH 6/8] h264_metadata: Remove unused fields

[Mark Thompson]

On 11/03/18 18:55, James Almer wrote:
> On 3/11/2018 3:30 PM, Mark Thompson wrote:
>> The SEI NAL is unused since 69062d0f9b6aef5d9d9b8c9c9b5cfb23037caddb,
>> while the AUD NAL is small and would more sensibly be on the stack.
>> ---
>>  libavcodec/h264_metadata_bsf.c | 12 +++++-------
>>  1 file changed, 5 insertions(+), 7 deletions(-)
>>
>> diff --git a/libavcodec/h264_metadata_bsf.c b/libavcodec/h264_metadata_bsf.c
>> index d340c55990..760fe99c41 100644
>> --- a/libavcodec/h264_metadata_bsf.c
>> +++ b/libavcodec/h264_metadata_bsf.c
>> @@ -47,9 +47,6 @@ typedef struct H264MetadataContext {
>>  
>>      int done_first_au;
>>  
>> -    H264RawAUD aud_nal;
>> -    H264RawSEI sei_nal;
>> -
>>      int aud;
>>  
>>      AVRational sample_aspect_ratio;
>> @@ -263,7 +260,9 @@ static int h264_metadata_filter(AVBSFContext *bsf, AVPacket *out)
>>                  0x3ff, // 0, 1, 2, 3, 4, 5, 6, 7, 8, 9
>>              };
>>              int primary_pic_type_mask = 0xff;
>> -            H264RawAUD *aud = &ctx->aud_nal;
>> +            H264RawAUD aud = {
>> +                .nal_unit_header.nal_unit_type = H264_NAL_AUD,
>> +            };
> 
> Afaik every other field is not zero initialized if you do this, unlike
> if you keep it in H264MetadataContext.
> Not sure if that may have some consequences or not here.

As long as one member is set the rest are are zero-initialised.

C11 §6.7.9, paragraph 19:
"all subobjects that are not initialized explicitly shall be initialized implicitly the same as
objects that have static storage duration."

(This is why the "{ 0 }" syntax works, because it initialises the first member to zero (whatever that is) and then the rest are implicitly zero as well.)

- Mark