[FFmpeg-devel] [PATCH] dxva2: bump maximum number of slieces for mpeg2

[Hendrik Leppkes]

On Mon, Jan 27, 2014 at 3:13 PM, compn <tempn at twmi.rr.com> wrote:
> On Mon, 27 Jan 2014 09:23:47 +0100
> Hendrik Leppkes <h.leppkes at gmail.com> wrote:
>
>> On Mon, Jan 27, 2014 at 8:22 AM, Rainer Hochecker
>> <fernetmenta at online.de> wrote:
>> > ---
>> >  libavcodec/dxva2_mpeg2.c | 2 +-
>> >  1 file changed, 1 insertion(+), 1 deletion(-)
>> >
>> > diff --git a/libavcodec/dxva2_mpeg2.c b/libavcodec/dxva2_mpeg2.c
>> > index 1827dd5..e2f6b70 100644
>> > --- a/libavcodec/dxva2_mpeg2.c
>> > +++ b/libavcodec/dxva2_mpeg2.c
>> > @@ -22,7 +22,7 @@
>> >
>> >  #include "dxva2_internal.h"
>> >
>> > -#define MAX_SLICES (SLICE_MAX_START_CODE - SLICE_MIN_START_CODE +
>> > 1) +#define MAX_SLICES 1024
>> >  struct dxva2_picture_context {
>> >      DXVA_PictureParameters pp;
>> >      DXVA_QmatrixData       qm;
>> > --
>> > 1.8.3.2
>> >
>>
>> Note that this value was empirically chosen, and there is no "spec" to
>> dictate the value.
>> The old MAX_SLICES was OK for SD content, but with HD and UHD content
>> files will have more slices, and so far 1024 was a safe limit with
>> plenty headroom to work on every file found.
>>
>> Another solution would be to dynamically allocate the slice array,
>> however since HWAccels don't have a global state to store the
>> information about the number of slices in, it would mean every frame
>> has to re-allocate the slice array hundreds of times, which is not
>> ideal.
>> The struct is  small enough to not worry about a few KB of memory
>> usage by the fixed-size array.
>
> +100 bonus points if you mention something like this in a comment in the
> patch.
>

Not my patch, I only suggested this solution to the problem. :)