[FFmpeg-devel] [PATCH 1/2] lavc/vaapi_encode: correct the HRD buffer size calculate.

[Jun Zhao]

On 2017/10/31 23:45, Mark Thompson wrote:
> On 31/10/17 15:11, Jun Zhao wrote:> On 2017/10/31 18:19, Mark Thompson wrote:
>>> On 31/10/17 02:37, Jun Zhao wrote:
>>>> From 7eef9be1c8a92bf625d62a0f97f762f1342c6d78 Mon Sep 17 00:00:00 2001
>>>> From: Jun Zhao <jun.zhao at intel.com>
>>>> Date: Tue, 31 Oct 2017 10:13:42 +0800
>>>> Subject: [PATCH 1/2] lavc/vaapi_encode: correct the HRD buffer size calculate.
>>>>
>>>> when rc_buffer_size didn't setting, always use the max bit rate
>>>> per second as HRD buffer size.
>>>>
>>>> Signed-off-by: Jun Zhao <jun.zhao at intel.com>
>>>> Signed-off-by: Wang, Yi A <yi.a.wang at intel.com>
>>>> ---
>>>>  libavcodec/vaapi_encode.c | 21 ++++++++++-----------
>>>>  1 file changed, 10 insertions(+), 11 deletions(-)
>>>>
>>>> diff --git a/libavcodec/vaapi_encode.c b/libavcodec/vaapi_encode.c
>>>> index 590f4be4ed..d5f89ef346 100644
>>>> --- a/libavcodec/vaapi_encode.c
>>>> +++ b/libavcodec/vaapi_encode.c
>>>> @@ -1144,19 +1144,9 @@ static av_cold int vaapi_encode_init_rate_control(AVCodecContext *avctx)
>>>>          return AVERROR(EINVAL);
>>>>      }
>>>>  
>>>> -    if (avctx->rc_buffer_size)
>>>> -        hrd_buffer_size = avctx->rc_buffer_size;
>>>> -    else
>>>> -        hrd_buffer_size = avctx->bit_rate;
>>>> -    if (avctx->rc_initial_buffer_occupancy)
>>>> -        hrd_initial_buffer_fullness = avctx->rc_initial_buffer_occupancy;
>>>> -    else
>>>> -        hrd_initial_buffer_fullness = hrd_buffer_size * 3 / 4;
>>>> -
>>>>      if (ctx->va_rc_mode == VA_RC_CBR) {
>>>>          rc_bits_per_second   = avctx->bit_rate;
>>>>          rc_target_percentage = 100;
>>>> -        rc_window_size       = 1000;
>>>>      } else {
>>>>          if (avctx->rc_max_rate < avctx->bit_rate) {
>>>>              // Max rate is unset or invalid, just use the normal bitrate.
>>>> @@ -1166,8 +1156,17 @@ static av_cold int vaapi_encode_init_rate_control(AVCodecContext *avctx)
>>>>              rc_bits_per_second   = avctx->rc_max_rate;
>>>>              rc_target_percentage = (avctx->bit_rate * 100) / rc_bits_per_second;
>>>>          }
>>>> -        rc_window_size = (hrd_buffer_size * 1000) / avctx->bit_rate;
>>>>      }
>>>> +    rc_window_size = (rc_bits_per_second * 1000) / avctx->bit_rate;
>>>> +
>>>> +    if (avctx->rc_buffer_size)
>>>> +        hrd_buffer_size = avctx->rc_buffer_size;
>>>> +    else
>>>> +        hrd_buffer_size = rc_bits_per_second;
>>>> +    if (avctx->rc_initial_buffer_occupancy)
>>>> +        hrd_initial_buffer_fullness = avctx->rc_initial_buffer_occupancy;
>>>> +    else
>>>> +        hrd_initial_buffer_fullness = hrd_buffer_size * 3 / 4;
>>>>  
>>>>      ctx->rc_params.misc.type = VAEncMiscParameterTypeRateControl;
>>>>      ctx->rc_params.rc = (VAEncMiscParameterRateControl) {
>>>> -- 
>>>> 2.14.1
>>>>
>>> Why?  If the RC buffer size is unset it currently guesses one second of the target bitrate - in what way is the peak bitrate any more appropriate as a guess?
>> In VBR mode, when rc_max_rate more than bit_rate, I think HDR size need
>> to use rc_max_rate, not the bit_rate.
> Ok, why do you think that?  I'm not necessarily against this change (in cases where it matters the user will provide rc_buffer_size explicitly), but please provide some reasoning for it.
I think the code logic have considered the explicit rc_buffer_size
setting, and this patch
correct the HRD buffer size with MAX(rc_max_rate, bit_rate) when no
setting rc_buffer_size in
VBR mode. In the old logic, in VBR mode, if user don't setting
rc_buffer_size
explicitly, the HRD buffer size always use avctx->bit_rate, it does not
make sense.
>
> - Mark
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