[FFmpeg-devel] [PATCH] libvpxenc: extend auto-alt-ref range

[James Zern]

On Sat, Nov 3, 2018 at 2:31 PM James Almer <jamrial at gmail.com> wrote:
>
> On 11/3/2018 6:04 PM, James Zern wrote:
> > On Sat, Nov 3, 2018 at 2:02 PM James Zern <jzern at google.com> wrote:
> >> [...]
> >>  #define COMMON_OPTIONS \
> >>      { "auto-alt-ref",    "Enable use of alternate reference " \
> >> -                         "frames (2-pass only)",                   OFFSET(auto_alt_ref),    AV_OPT_TYPE_INT, {.i64 = -1},      -1,      2,       VE}, \
> >> +                         "frames (2-pass only)",                   OFFSET(auto_alt_ref),    AV_OPT_TYPE_INT, {.i64 = -1},      -1,      6,       VE}, \
> >
> > This was extended earlier [1], but probably should have been made
> > codec specific. I can do that, but we might want to keep the 0-2 range
> > for vp8 now for compatibility. Any preferences?
>
> What happens when you use the higher values while encoding VP8? Does it
> error out or silently clips it to 1 internally?
>
> If it errors out then yes, move it out of COMMON_OPTIONS and into each
> encoder AVOption array.
>

VP8 is clipped in this file currently because the library will error
out with values > 1:
        codecctl_int(avctx, VP8E_SET_ENABLEAUTOALTREF,
                     avctx->codec_id == AV_CODEC_ID_VP8 ?
!!ctx->auto_alt_ref : ctx->auto_alt_ref);

So moving it from COMMON_OPTIONS at this point will avoid any more
drift in the reported range of '-h encoder=libvpx'.

> >
> > [1] 41da4f8cb3 lavc/libvpxenc: fix -auto-alt-ref option type
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> >
>
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