[FFmpeg-devel] [PATCH] avcodec/mpeg4videodec: Add support for parsing and exporting video_range

[Mark Thompson]

On 10/12/17 21:49, Michael Niedermayer wrote:
> On Sun, Dec 10, 2017 at 07:56:49PM +0000, Mark Thompson wrote:
>> On 10/12/17 15:20, Michael Niedermayer wrote:
>>> Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
>>> ---
>>>  libavcodec/mpeg4video.h    |  3 +++
>>>  libavcodec/mpeg4videodec.c | 32 ++++++++++++++++++++++++++++++++
>>>  2 files changed, 35 insertions(+)
>>>
>>> diff --git a/libavcodec/mpeg4video.h b/libavcodec/mpeg4video.h
>>> index 515b008ae4..0ba502d50b 100644
>>> --- a/libavcodec/mpeg4video.h
>>> +++ b/libavcodec/mpeg4video.h
>>> @@ -43,6 +43,9 @@
>>>  #define ACE_VO_TYPE             12
>>>  #define ADV_SIMPLE_VO_TYPE      17
>>>  
>>> +#define VOT_VIDEO_ID 1
>>> +#define VOT_STILL_TEXTURE_ID 2
>>> +
>>>  // aspect_ratio_info
>>>  #define EXTENDED_PAR 15
>>>  
>>> diff --git a/libavcodec/mpeg4videodec.c b/libavcodec/mpeg4videodec.c
>>> index cdd7077f01..852f73f02c 100644
>>> --- a/libavcodec/mpeg4videodec.c
>>> +++ b/libavcodec/mpeg4videodec.c
>>> @@ -1751,6 +1751,36 @@ static int mpeg4_decode_profile_level(MpegEncContext *s, GetBitContext *gb)
>>>          s->avctx->level = 0;
>>>      }
>>>  
>>> +    return 0;
>>> +
>>
>> Stray newline.
>>
>>> +}
>>> +
>>> +static int mpeg4_decode_visual_object(MpegEncContext *s, GetBitContext *gb)
>>> +{
>>> +    int visual_object_type;
>>> +    int is_visual_object_identifier = get_bits1(gb);
>>> +
>>> +    if (is_visual_object_identifier) {
>>> +        skip_bits(gb, 4+3);
>>> +    }
>>> +    visual_object_type = get_bits(gb, 4);
>>> +
>>> +    if (visual_object_type == VOT_VIDEO_ID ||
>>> +        visual_object_type == VOT_STILL_TEXTURE_ID) {
>>> +        int video_signal_type = get_bits1(gb);
>>> +        if (video_signal_type) {
>>> +            int video_format = get_bits(gb, 3);
>>> +            int video_range = get_bits1(gb);
>>> +            int color_description = get_bits1(gb);
>>> +
>>> +            s->avctx->color_range = video_range ? AVCOL_RANGE_JPEG : AVCOL_RANGE_MPEG;
>>> +
>>> +            if (color_description) {
>>> +                skip_bits(gb, 8+8+8);
>>
>> Might be nice to extract the colour information as well?  (Should be able to set color_primaries/color_trc/colorspace directly, I think.)
> 
> will look into this
> btw, iam a bit short on samples that use this
> i had found just one sample after a quick look
> more samples would be welcome, if someone has some.

>From a quick look around (run over some MPEG-4 samples with an abort in the above code) I can't find any examples of video_signal_type being set at all.  Minor thing I noticed in doing that - video_format is unused so you get a warning from the compiler: since it's not useful to anyone maybe replace it with skip_bits(3) and move the other stuff around to match that?

Don't block this because of the colour part if you don't have a sample of that - I just thought from reading the relevant part of the standard that it should be easy, but if noone has ever used it then whatever.

Thanks,

- Mark