[FFmpeg-devel] [PATCH 5/8] avcodec/av1dec: parse dimensions from the sequence header in extradata

[James Almer]

On 9/29/2020 12:52 PM, Mark Thompson wrote:
> On 25/09/2020 15:43, James Almer wrote:
>> Signed-off-by: James Almer <jamrial at gmail.com>
>> ---
>>   libavcodec/av1dec.c | 10 ++++++++++
>>   1 file changed, 10 insertions(+)
>>
>> diff --git a/libavcodec/av1dec.c b/libavcodec/av1dec.c
>> index 0bb04a3e44..f6b9fbbac3 100644
>> --- a/libavcodec/av1dec.c
>> +++ b/libavcodec/av1dec.c
>> @@ -405,6 +405,9 @@ static av_cold int av1_decode_free(AVCodecContext
>> *avctx)
>>   static int set_context_with_sequence(AVCodecContext *avctx,
>>                                        const AV1RawSequenceHeader *seq)
>>   {
>> +    int width = seq->max_frame_width_minus_1 + 1;
>> +    int height = seq->max_frame_height_minus_1 + 1;
>> +
>>       avctx->profile = seq->seq_profile;
>>       avctx->level = seq->seq_level_idx[0];
>>   @@ -423,6 +426,13 @@ static int
>> set_context_with_sequence(AVCodecContext *avctx,
>>           break;
>>       }
>>   +    if (avctx->width != width || avctx->height != height) {
>> +        int ret = ff_set_dimensions(avctx, width, height);
>> +        if (ret < 0)
>> +            return ret;
>> +    }
>> +    avctx->sample_aspect_ratio = (AVRational) { 1, 1 };
>> +
>>       if (seq->timing_info.num_units_in_display_tick &&
>>           seq->timing_info.time_scale) {
>>           av_reduce(&avctx->framerate.den, &avctx->framerate.num,
>>
> 
> Can you explain more about why this might be wanted?  There is no
> requirement that the stream actually contains any frames with the size
> stated in the sequence header.

It gives you an AVCodecContext with enough parameters for most non
decoding scenarios immediately after avcodec_open2(). They will be
updated with frame dimensions afterwards if any is parsed.
Also, the AVCodecContext dimension fields are nonetheless documented to
not necessarily match the latest returned frame's dimensions.

Applying this set without this patch, if this is the only decoder
available and is therefore used for probing, some of the remuxing FATE
tests will fail once a pix_fmt is not assigned and frames are then not
parsed.

> 
> - Mark
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