On 21/08/17 02:09, Michael Niedermayer wrote:
> On Sun, Aug 20, 2017 at 11:41:30PM +0100, Mark Thompson wrote:
>> With comments describing the derivation of each value.
>>
>> (cherry picked from commit aaf441465080b9bc57f5ca8dea656f9b2c5dc821)
>> ---
>> libavcodec/h264.h | 45 +++++++++++++++++++++++++++++++++++++++++++++
>> 1 file changed, 45 insertions(+)
>>
>> diff --git a/libavcodec/h264.h b/libavcodec/h264.h
>> index 86df5eb9b3..650580bf3a 100644
>> --- a/libavcodec/h264.h
>> +++ b/libavcodec/h264.h
>> @@ -44,4 +44,49 @@ enum {
>> H264_NAL_AUXILIARY_SLICE = 19,
>> };
>>
>> +
>> +enum {
>
> why is this a enum ?
I believe that compile-time symbolic constants are preferable to preprocessor
string replacement.
>> + // 7.4.2.1.1: seq_parameter_set_id is in [0, 31].
>> + H264_MAX_SPS_COUNT = 32,
>
> Could be doxygen comment compatible
Would that have any value? The comments are explaining the derivation for
verification purposes rather than anything to do with the actual use.
>> + // A.3: in table A-1 the highest level allows a MaxFS of 139264.
>> + H264_MAX_MB_PIC_SIZE = 139264,
>> + // A.3.1, A.3.2: PicWidthInMbs and PicHeightInMbs are constrained
>> + // to be not greater than sqrt(MaxFS * 8). Hence height/width are
>> + // bounded above by sqrt(139264 * 8) = 1055.5 macroblocks.
>> + H264_MAX_MB_WIDTH = 1055,
>> + H264_MAX_MB_HEIGHT = 1055,
>> + H264_MAX_WIDTH = H264_MAX_MB_WIDTH * 16,
>> + H264_MAX_HEIGHT = H264_MAX_MB_HEIGHT * 16,
>
> There should be no problem with files outside these limits. They would
> be valid H.264 files, just not within the level and profile constraints
> of the currently defined profiles and levels.
> or do i miss something ?
Currently these values are used for some fixed-size tables in cbs (e.g.
H264_MAX_MB_PIC_SIZE is needed for slice_group_id[]). More generally, I don't
want to consider files which don't conform to some level limits - once you
allow MaxDPBFrames to exceed 16 the world is a terrible place.
(I am not intending to add this constraint to the existing decoder.)
Thanks,
- Mark
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