On 04/26/2016 08:49 AM, Kal Sze wrote:
> And what is the valid number of slices when encoding as FFV1 level 3?
> The wiki says 4, 6, 9, 12, 16, 24, or 30; but I have not seen ffmpeg
> complain if I try to specify something like 25 slices for a 512x424
> video. Does ffmpeg just coerce the value to a valid one?
As far as I know, slices must be a number that allows the image to be
evenly divided in.
For example 25 slices = 5*5 - so it's fine.
FFmpeg usually throws an error if the slice number doesn't make sense.
It does not coerce that value to a valid one.
Here's the part of ffv1enc.c that decides whether the number of slices
is good or not:
[quote]
s->num_v_slices = (avctx->width > 352 || avctx->height > 288 ||
!avctx->slices) ? 2 : 1;
for (; s->num_v_slices < 9; s->num_v_slices++) {
for (s->num_h_slices = s->num_v_slices; s->num_h_slices <
2*s->num_v_slices; s->num_h_slices++) {
if (avctx->slices == s->num_h_slices * s->num_v_slices
&& avctx->slices <= 64 || !avctx->slices)
goto slices_ok;
}
}
av_log(avctx, AV_LOG_ERROR,
"Unsupported number %d of slices requested, please
specify a "
"supported number with -slices (ex:4,6,9,12,16, ...)\n",
avctx->slices);
[/quote]
If I read the code correctly, there's also a condition slices must also
not exceed 64.
Kind regards,
Pb
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