Re: [FFmpeg-devel] [PATCH] avformat/apvdec: export color information

[James Almer <jamrial@gmail.com>]

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On 4/27/2025 3:29 PM, Mark Thompson wrote:
> On 27/04/2025 18:53, James Almer wrote:
>> apv_read_header() reads enough information that the generic demux code doesn't
>> attempt to read a frame to fill missing fields in codecpar, so make sure it's
>> set here.
>>
>> Signed-off-by: James Almer <jamrial@gmail.com>
>> ---
>>   libavformat/apvdec.c | 32 +++++++++++++++++++++++++++++---
>>   1 file changed, 29 insertions(+), 3 deletions(-)
>>
>> diff --git a/libavformat/apvdec.c b/libavformat/apvdec.c
>> index e1ac34b003..94d2ce9965 100644
>> --- a/libavformat/apvdec.c
>> +++ b/libavformat/apvdec.c
>> @@ -39,6 +39,11 @@ typedef struct APVHeaderInfo {
>>       uint8_t  chroma_format_idc;
>>       uint8_t  bit_depth_minus8;
>>   
>> +    int      color_primaries;
>> +    int      transfer_characteristics;
>> +    int      matrix_coefficients;
>> +    int      full_range_flag;
>> +
>>       enum AVPixelFormat pixel_format;
>>   } APVHeaderInfo;
>>   
>> @@ -55,6 +60,8 @@ static int apv_extract_header_info(APVHeaderInfo *info,
>>   {
>>       int zero, byte, bit_depth_index;
>>   
>> +    memset(info, 0, sizeof(*info));
>> +
>>       info->pbu_type = bytestream2_get_byte(gbc);
>>       info->group_id = bytestream2_get_be16(gbc);
>>   
>> @@ -107,10 +114,24 @@ static int apv_extract_header_info(APVHeaderInfo *info,
>>       // Ignore capture_time_distance.
>>       bytestream2_skip(gbc, 1);
>>   
>> -    zero = bytestream2_get_byte(gbc);
>> -    if (zero != 0)
>> +    // two reserved_zero_8bits
>> +    if (bytestream2_get_be16(gbc) != 0)
>>           return AVERROR_INVALIDDATA;
>>   
>> +    // color_description_present_flag
>> +    if (bytestream2_peek_byte(gbc) >> 7) {
>> +        // We can read 32 bits as tile info is guaranteed to be present after this.
>> +        unsigned color_description = bytestream2_get_be32(gbc);
>> +
>> +        if (bytestream2_get_bytes_left(gbc) <= 0)
>> +            return AVERROR_INVALIDDATA;
>> +
>> +        info->color_primaries          = (color_description >> 23) & 0xff;
>> +        info->transfer_characteristics = (color_description >> 15) & 0xff;
>> +        info->matrix_coefficients      = (color_description >>  7) & 0xff;
> 
> For these "unspecified" has value 2, which will need to be set somewhere in no-description case rather than zero-init.  (Matrix coefficients 0 means identity, i.e. RGB, which we definitely don't want.)

Ok.

> 
>> +        info->full_range_flag          = (color_description >>  6) & 1;
>> +    }
>> +
>>       return 1;
>>   }
>>   
>> @@ -157,7 +178,7 @@ static int apv_read_header(AVFormatContext *s)
>>       AVStream *st;
>>       GetByteContext gbc;
>>       APVHeaderInfo header;
>> -    uint8_t buffer[28];
>> +    uint8_t buffer[64];
> 
> Could be smaller, but doesn't really matter.

Will make it smaller.

> 
>>       uint32_t au_size, signature, pbu_size;
>>       int err, size;
>>   
>> @@ -201,6 +222,11 @@ static int apv_read_header(AVFormatContext *s)
>>       st->codecpar->level      = header.level_idc;
>>       st->codecpar->width      = header.frame_width;
>>       st->codecpar->height     = header.frame_height;
>> +    st->codecpar->color_primaries = header.color_primaries;
>> +    st->codecpar->color_trc       = header.transfer_characteristics;
>> +    st->codecpar->color_space     = header.matrix_coefficients;
>> +    st->codecpar->color_range     = header.full_range_flag ? AVCOL_RANGE_JPEG
>> +                                                           : AVCOL_RANGE_MPEG;
> 
> Suggest st->codecpar->chroma_location = AVCHROMA_LOC_TOPLEFT as well?

Sure.

> 
>>   
>>       st->avg_frame_rate = (AVRational){ 30, 1 };
>>       avpriv_set_pts_info(st, 64, 1, 30);
> 
> Thanks,
> 
> - Mark
> 
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