[FFmpeg-devel] [PATCH] Set generic yuv420 sampling in yuv4mpeg by default

[David Conrad]

On May 9, 2009, at 11:04 PM, Michael Niedermayer wrote:

> On Sat, May 09, 2009 at 08:05:02PM -0400, David Conrad wrote:
>> On May 9, 2009, at 6:29 AM, Michael Niedermayer wrote:
>>
>>> On Sat, May 09, 2009 at 05:48:30AM -0400, David Conrad wrote:
>>>> On May 8, 2009, at 9:49 AM, Michael Niedermayer wrote:
>>>>
>>>>> On Thu, May 07, 2009 at 11:43:25PM -0400, David Conrad wrote:
>>>>>> Hi,
>>>>>>
>>>>>> As discovered in #x264, the dump_psnr tool in Thusnelda  
>>>>>> actually cares
>>>>>> about chroma sample positions. This should probably be more  
>>>>>> correct; I
>>>>>> don't know for sure which codecs define which positioning.
>>>>>
>>>>> many codecs leave it unspecified
>>>>> h264 & mpeg4 match mpeg2 by default in theory, in how far the  
>>>>> actual
>>>>> data matches this of course is another question
>>>>
>>>> I didn't know that; but probably the correlation with actual data  
>>>> isn't
>>>> much worse than mpeg2.
>>>
>>> maybe
>>>
>>>>> h264 allows the exact chroma positions to be stored for 420
>>>>> we could add a chroma_sample_location field to AVCodecContext  
>>>>> maybe
>>>>
>>>> I wound up doing this and adding values for a couple codecs I  
>>>> looked up.
>>>>
>>>
>> commit f08dcb90cda6fa44c91cdefa917d2dd0d57cd497
>> Author: David Conrad <lessen42 at gmail.com>
>> Date:   Sat May 9 19:57:11 2009 -0400
>>
>>    Add a chroma_sample_location field to define positioning of  
>> chroma samples
>>
>> diff --git a/libavcodec/avcodec.h b/libavcodec/avcodec.h
>> index 4226673..a733a33 100644
>> --- a/libavcodec/avcodec.h
>> +++ b/libavcodec/avcodec.h
>> @@ -479,6 +479,21 @@ enum AVColorRange{
>>     AVCOL_RANGE_NB           , ///< Not part of ABI
>> };
>>
>> +/**
>> + *  X   X      3 4 X      X are luma samples,
>> + *             1 2        1-6 are possible chroma positions
>> + *  X   X      5 6 X      0 is undefined/unknown position
>> + */
>> +enum AVChromaLocation{
>> +    AVCHROMA_LOC_UNSPECIFIED=0,
>> +    AVCHROMA_LOC_LEFT       =1, ///< mpeg2/4, h264 default
>> +    AVCHROMA_LOC_CENTER     =2, ///< mpeg1, jpeg, h263
>> +    AVCHROMA_LOC_TOPLEFT    =3, ///< DV
>> +    AVCHROMA_LOC_TOP        =4,
>> +    AVCHROMA_LOC_BOTTOMLEFT =5,
>> +    AVCHROMA_LOC_BOTTOM     =6,
>> +};
>> +
>> typedef struct RcOverride{
>>     int start_frame;
>>     int end_frame;
>> @@ -2481,6 +2496,13 @@ typedef struct AVCodecContext {
>>      * - decoding: Set by libavcodec
>>      */
>>     enum AVColorRange color_range;
>> +
>> +    /**
>> +     * This defines the location of chroma samples.
>> +     * - encoding: Set by user
>> +     * - decoding: Set by libavcodec
>> +     */
>> +     enum AVChromaLocation chroma_sample_location;
>> } AVCodecContext;
>
> update to the AVOptions array is missing

Fixed.

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