[FFmpeg-devel] [PATCH] libavcodec/libx264: fix reference frame computation based on level

[Fu, Linjie]

Hi,

> From: ffmpeg-devel <ffmpeg-devel-bounces at ffmpeg.org> On Behalf Of
> josh.brewster at protonmail.com
> Sent: Friday, April 17, 2020 07:05
> To: ffmpeg-devel at ffmpeg.org
> Subject: [FFmpeg-devel] [PATCH] libavcodec/libx264: fix reference frame
> computation based on level
> 
> Hell, can someone please review this patch? It fixes a wrong reference frame
> computation problem when using parameters such as "-level 31" instead of
> "-level 3.1".
>
> diff --git a/libavcodec/libx264.c b/libavcodec/libx264.c
> index a08fe0ce76..1149f2d668 100644
> --- a/libavcodec/libx264.c
> +++ b/libavcodec/libx264.c
> @@ -701,11 +701,14 @@ FF_ENABLE_DEPRECATION_WARNINGS
> 
>          if (!strcmp(x4->level, "1b")) {
>              level_id = 9;
> -        } else if (strlen(x4->level) <= 3){
> +        } else if (av_strtod(x4->level, NULL) < 7){
>              level_id = av_strtod(x4->level, &tail) * 10 + 0.5;
>              if (*tail)
>                  level_id = -1;
>          }
> +        else {
Wrong coding style for "else", should be "} else {"
> +            level_id = av_strtod(x4->level, NULL);
> +        }
>          if (level_id <= 0)
>              av_log(avctx, AV_LOG_WARNING, "Failed to parse level\n");

This part of code of parsing level_id seems redundant, since PARSE_X264_OPT("level", level) has
been called  and did  the same thing inside libx264, which converts x4->level to x4->params.i_level_idc
correctly (equals 31), regardless of "-level 3.1 or level 31".

Hence it would be better to use x4->params.i_level_idc directly.

- Linjie