[FFmpeg-devel] [PATCH 2/3] mpegvideo_parser: parse the output picture number

Michael Niedermayer michael at niedermayer.cc
Wed Mar 7 02:55:29 EET 2018

On Sun, Feb 11, 2018 at 08:31:40PM +0200, Jan Ekström wrote:
> On Sun, Feb 11, 2018 at 7:52 PM, Michael Niedermayer
> <michael at niedermayer.cc> wrote:
> >
> > should be ok unless its intended to also restore the MSB
> >
> The value seemed to be 10bit and if the pointer is at the position
> right after the picture_start_code, then `buf[0] << 2` would move the
> 8 bits left of data two bits leftwards, and `buf[1] >> 6` would then
> move the topmost bits of the following byte to be the bottom-most
> bits.
> Unless you mean that there's a forgotten `(uint16_t)` there as the end
> value has 10 bits of effective data, making the correct way of doing
> it something a la `(((uint16_t)buf[0]) << 2) | (((uint16_t)buf[1]) >>
> 6)`?

it was more a question about our API 

if output_picture_number is intended to be what it is called in english then
this patch is wrong as the number will frequently go back to 0 and
as more than 1024 pictures are output.
so taken as its english meaning, there would be code needed to increase(/decrease)
the MSB occasionally
OTOH if the field is intended to store a unspecified number of LSB only
i wonder what it could be used for

> > Theres no code using output_picture_number currently
> >
> Seems like some API users utilize this value.

What do they do with it ?


Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Avoid a single point of failure, be that a person or equipment.
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