Re: [FFmpeg-devel] [PATCH] lavc/qsvenc: Set default bitrate to 2M

[Zhao Zhili <quinkblack@foxmail.com>]

> On Dec 6, 2023, at 20:26, Timo Rothenpieler <timo@rothenpieler.org> wrote:
> 
> On 06/12/2023 07:51, Xiang, Haihao wrote:
>> On Di, 2023-12-05 at 12:47 +0100, Timo Rothenpieler wrote:
>>> On 05.12.2023 09:15, Xiang, Haihao wrote:
>>>> From: Haihao Xiang <haihao.xiang@intel.com>
>>>> 
>>>> 2M is suitable for more cases, e.g. 4K video.
>>>> 
>>>> Signed-off-by: Haihao Xiang <haihao.xiang@intel.com>
>>>> ---
>>>>   libavcodec/qsvenc_av1.c   | 2 +-
>>>>   libavcodec/qsvenc_h264.c  | 2 +-
>>>>   libavcodec/qsvenc_hevc.c  | 2 +-
>>>>   libavcodec/qsvenc_mpeg2.c | 2 +-
>>>>   libavcodec/qsvenc_vp9.c   | 2 +-
>>>>   5 files changed, 5 insertions(+), 5 deletions(-)
>>>> 
>>>> diff --git a/libavcodec/qsvenc_av1.c b/libavcodec/qsvenc_av1.c
>>>> index c697845d7b..78c92c1844 100644
>>>> --- a/libavcodec/qsvenc_av1.c
>>>> +++ b/libavcodec/qsvenc_av1.c
>>>> @@ -129,7 +129,7 @@ static const AVClass class = {
>>>>   };
>>>>      static const FFCodecDefault qsv_enc_defaults[] = {
>>>> -    { "b",         "1M"   },
>>>> +    { "b",         "2M"   },
>>> 
>>> Wouldn't it be better to use a constant quality option as default,
>>> rather than a fixed bitrate?
>> Did you mean change the default bitrate control mode to CQP ? I was concerned
>> about the impact to current users.
> 
> Yeah, it's technically a breaking change.
> Though at least libx264 also at some point changed its default to a reasonable medium quality crf mode, away from a fixed, rather low, bitrate.
> Not sure if that was done on a major bump, or if it was considered low impact enough to just push out.
> 
>>> 2M still seems incredibly low for 1080p, let alone for 4K content.
>> Some other HW encoders also use 2M, I'd like to use the same default value.
> 
> It's probably worth considering switching those to a crf equivalent as well, where possible.
> It matches much more what a typical user would expect if they input a commandline with no further options.

Without a strategy to adapt to different needs automatically like crf, I prefer error out than
a default bitrate TBH. Of course we cannot do that now since it will suddenly  break current
use cases. How about set default bitrate to zero, then add a warning message if user don’t
change it, then set bitrate to any default/heuristics value?

> 
>> Thanks
>> Haihao
>>> 
>>>>       { "g",         "-1"   },
>>>>       { "bf",        "-1"   },
>>>>       { "refs",      "0"    },
>>>> diff --git a/libavcodec/qsvenc_h264.c b/libavcodec/qsvenc_h264.c
>>>> index 071a9a79e9..37b39cb441 100644
>>>> --- a/libavcodec/qsvenc_h264.c
>>>> +++ b/libavcodec/qsvenc_h264.c
>>>> @@ -178,7 +178,7 @@ static const AVClass class = {
>>>>   };
>>>>      static const FFCodecDefault qsv_enc_defaults[] = {
>>>> -    { "b",         "1M"    },
>>>> +    { "b",         "2M"    },
>>>>       { "refs",      "0"     },
>>>>       { "g",         "-1"    },
>>>>       { "bf",        "-1"    },
>>>> diff --git a/libavcodec/qsvenc_hevc.c b/libavcodec/qsvenc_hevc.c
>>>> index c5b7ac7cc4..181d06cb00 100644
>>>> --- a/libavcodec/qsvenc_hevc.c
>>>> +++ b/libavcodec/qsvenc_hevc.c
>>>> @@ -374,7 +374,7 @@ static const AVClass class = {
>>>>   };
>>>>      static const FFCodecDefault qsv_enc_defaults[] = {
>>>> -    { "b",         "1M"    },
>>>> +    { "b",         "2M"    },
>>>>       { "refs",      "0"     },
>>>>       { "g",         "248"   },
>>>>       { "bf",        "-1"    },
>>>> diff --git a/libavcodec/qsvenc_mpeg2.c b/libavcodec/qsvenc_mpeg2.c
>>>> index 22f1ff7c0d..012cec3a58 100644
>>>> --- a/libavcodec/qsvenc_mpeg2.c
>>>> +++ b/libavcodec/qsvenc_mpeg2.c
>>>> @@ -82,7 +82,7 @@ static const AVClass class = {
>>>>   };
>>>>      static const FFCodecDefault qsv_enc_defaults[] = {
>>>> -    { "b",         "1M"    },
>>>> +    { "b",         "2M"    },
>>>>       { "refs",      "0"     },
>>>>       // same as the x264 default
>>>>       { "g",         "250"   },
>>>> diff --git a/libavcodec/qsvenc_vp9.c b/libavcodec/qsvenc_vp9.c
>>>> index d0340ef94b..8658b8ec2d 100644
>>>> --- a/libavcodec/qsvenc_vp9.c
>>>> +++ b/libavcodec/qsvenc_vp9.c
>>>> @@ -93,7 +93,7 @@ static const AVClass class = {
>>>>   };
>>>>      static const FFCodecDefault qsv_enc_defaults[] = {
>>>> -    { "b",         "1M"    },
>>>> +    { "b",         "2M"    },
>>>>       { "refs",      "0"     },
>>>>       { "g",         "250"   },
>>>>       { "trellis",   "-1"    },
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