On 29-08-2025 16:53, Nicolas Gaullier via ffmpeg-user wrote:
On 8/29/25 15:17, Hervé ANSELME wrote:
Hi,
I guess there is also a ffmpeg issue, because with the libsvtav1 codec :
-> if I use the ffmpeg 6.1 release : the "-maxrate" parameter is allowed
-> whereas if I use the 8.0 release : the "-maxrate" parameter
triggers an error
and this, with the same video codec, libsvtav1.
That's why, in the command line below, there is no "-maxrate"
parameter : because it was with the 8.0 release.
Regards,
HA
------------------------------------------------------------------------
*From:* Nicolas Gaullier via ffmpeg-user <ffmpeg-user@ffmpeg.org>
*Sent:* Friday, August 29, 2025 13:51
Hello,
AFAIK, this is a libsvtav1 issue, not an ffmpeg issue.
The kind of setup and target you have is possible with libx264, for
example, but not with libsvtav1.
You can give a try to the CBR mode of libsvtav1, but it is very
restricted, it involves the low delay mode, I feel you won't be very
happy with the resulting quality, but actually you should obtain the
desired bitrate.
Nicolas
On 8/29/25 10:03, Hervé ANSELME via ffmpeg-user wrote:
>
> Hello all,
>
> I am using the release 8.0 of ffmpeg/ffprobe, running on Windows 11
Family OS.
>
> I executed the following command :
>
> ffmpeg -i "initial movie.mkv" -y -loglevel error -sn ^
> -map 0:a:0 -acodec aac -ar 44100 -b:a 128k ^
> -map 0:v:0 -vcodec libsvtav1 -vf "scale=768:432" -sws_flags
lanczos+accurate_rnd -b:v 1200k -minrate 1200k ^
> -svtav1-params
"lossless=lower:nal-hrd=cbr:force-cfr=1:vbv-maxrate=1200k:vbv-bufsize=2400k"
^
> -bufsize 2400k "final movie.mkv"
>
> then, to see the result in the final film, regarding the video
characteristics, I executed :
>
> ffprobe -v error -select_streams v -show_entries
stream=codec_name,width,height,avg_frame_rate -of
default=noprint_wrappers=1 "final movie.mkv"
>
> which result is :
>
> bit_rate=930911
> codec_name=av1
> width=768
> height=432
> avg_frame_rate=25/1
>
> which raises the question : how is it that there is such a large
difference, between the desired video bitrate (1200k) and the actual
video bitrate obtained (930911 = 930k) ?
>
> How should I modify my command line to obtain an effective video
bitrate that is, if not equal, at least as close as possible, to 1200k ?
>
> Thank you in advance for your replies and advices.
>
> Cdlt,
> HA
Hum, we are both top-posting, which is very bad, let's back to the ML
rules...
Well, I tried your command line with "maxrate" added, and the log
seems pretty clear:
"Svt[error]: Instance 1: Max Bitrate only supported with CRF mode"
So, bad settings and clear error message: there is no ffmpeg issue, here.
NB1: libsvtav1 is somewhat picky with its settings, be careful about
it, look for example at the source here:
https://gitlab.com/AOMediaCodec/SVT-AV1/-/blob/master/Docs/Parameters.md
NB2: For future support queries, please make sure there is no error in
your command line before posting. I mean, you should have noted the
"Error parsing option lossless: lower" etc., so please remove any
extraneous/confusing/unsupported parameter even if it is not the root
of the issue you ask support for.
Nicolas
The SVT-AV1 rate cotrol documentation has this in it:
"If the maximum bit rate is set to a high value, the CRF and capped CRF
might produce the same results."
It simply means that the specified bitrate was too high for the encoded
content with the given buffersize and was lowered to adjust for that.
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