[FFmpeg-devel] [PATCH] avcodec/h264_slice: clear old slice POC values on parsing failure

[James Almer]

On 8/10/2021 12:04 PM, Andreas Rheinhardt wrote:
> James Almer:
>> If a slice header fails to parse, and the next one uses different Sequence and
>> Picture parameter sets, certain values may not be read if they are not coded,
>> resulting in the previous slice values being used.
>>
>> Signed-off-by: James Almer <jamrial at gmail.com>
>> ---
>>   libavcodec/h264_slice.c | 3 +++
>>   1 file changed, 3 insertions(+)
>>
>> diff --git a/libavcodec/h264_slice.c b/libavcodec/h264_slice.c
>> index 41338fbcb6..a31e804620 100644
>> --- a/libavcodec/h264_slice.c
>> +++ b/libavcodec/h264_slice.c
>> @@ -1897,6 +1897,8 @@ static int h264_slice_header_parse(const H264Context *h, H264SliceContext *sl,
>>       if (nal->type == H264_NAL_IDR_SLICE)
>>           get_ue_golomb_long(&sl->gb); /* idr_pic_id */
>>   
>> +    sl->poc_lsb = 0;
>> +    sl->delta_poc_bottom = 0;
>>       if (sps->poc_type == 0) {
>>           sl->poc_lsb = get_bits(&sl->gb, sps->log2_max_poc_lsb);
>>   
>> @@ -1904,6 +1906,7 @@ static int h264_slice_header_parse(const H264Context *h, H264SliceContext *sl,
>>               sl->delta_poc_bottom = get_se_golomb(&sl->gb);
>>       }
>>   
>> +    sl->delta_poc[0] = sl->delta_poc[1] = 0;
>>       if (sps->poc_type == 1 && !sps->delta_pic_order_always_zero_flag) {
>>           sl->delta_poc[0] = get_se_golomb(&sl->gb);
>>   
>>
> Does this patch actually change anything when all SPS use
> pic_ordering_cnt_type 0?

No, all these fields are zero initialized by the decoder, and inferred 
to 0 when not present.

> 
> - Andreas
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