[FFmpeg-devel] [PATCH 2/2] lavf/vaapi_encode: fix to set the default max bitrate for AVC VBR

[Mark Thompson]

On 12/03/18 05:38, Pengfei Qu wrote:
>     And for VBR mode, generally the max bit rate is bigger than the taraget
>     bitrate. For CBR mode, the max bitrate is same as the target bitrate.
>      when there is no specfic setting for the max bit rate parameter,
>     here the default value 95% is used to caculate the default max bitrate accordingly.
> 
> Signed-off-by: Pengfei Qu <Pengfei.Qu at intel.com>
> ---
>  libavcodec/vaapi_encode.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/libavcodec/vaapi_encode.c b/libavcodec/vaapi_encode.c
> index 78347d4..47110cf 100644
> --- a/libavcodec/vaapi_encode.c
> +++ b/libavcodec/vaapi_encode.c
> @@ -1164,8 +1164,8 @@ static av_cold int vaapi_encode_init_rate_control(AVCodecContext *avctx)
>      } else {
>          if (avctx->rc_max_rate < avctx->bit_rate) {
>              // Max rate is unset or invalid, just use the normal bitrate.
> -            rc_bits_per_second   = avctx->bit_rate;
> -            rc_target_percentage = 100;
> +            rc_target_percentage = 95;
> +            rc_bits_per_second   = (unsigned long)(avctx->bit_rate * 100.0 / rc_target_percentage);
>          } else {
>              rc_bits_per_second   = avctx->rc_max_rate;
>              rc_target_percentage = (unsigned long)(avctx->bit_rate * 100) / rc_bits_per_second;
> 

Can you give more detail about the motivation for this change?

In particular:
* You say you are fixing something - what is the issue?
* Where has the 95% number come from?
* Do you want this to apply to all codecs?  (The commit message says AVC.)

- Mark