[FFmpeg-user] FFmpeg's H264 and HEVC QSV encoder wrappers not obeying the set GOP size parameter value via -g:v

[Dennis Mungai]

On Mon, 18 Dec 2023 at 00:55, Dennis Mungai <dmngaie at gmail.com> wrote:

> Hello there,
>
> As tested with FFmpeg 6.1 and git tip master, FFmpeg's H.264 and HEVC QSV
> encoder wrappers, ie h264_qsv and hevc_qsv are not accepting the configured
> GOP size(s) set via the generic option -g:v.
>
> A trivial command such as the one shows below demonstrates the failure:
>
> ffmpeg -thread_queue_size 5120 -nostdin -y -fflags +genpts -y \
> -init_hw_device vaapi=va:/dev/dri/renderD129 \
> -init_hw_device qsv=qs at va \
> -filter_hw_device qs \
> -extra_hw_frames 64 \
> -threads:v 2 -async 1 \
> -probesize 10M -analyzeduration 10M \
> -f mpegts -fix_teletext_pts 1 -scan_all_pmts 1 -merge_pmt_versions 1 \
> -i "input.ts" \
> -vf 'hwmap=derive_device=qsv,format=qsv,vpp_qsv=deinterlace=2:scale_mode=0:async_depth=4' \
> -sc_threshold 0 -strict -1 -bitrate_limit:v 0 -g:v 50 -async_depth:v 4 -look_ahead_depth:v 40 \
> -preset:v medium -refs:v 5 -extbrc:v 1 -bf:v 0 -low_power:v 1 -r:v 25 \
> -b:v 4500k -minrate:v 4500k -maxrate:v 4500k -bufsize:v 9000k -rc_init_occupancy:v 4500k -c:v h264_qsv \
> -c:a aac -ac 2 -b:a 128k \
> -flags -global_header+cgop -max_muxing_queue_size 2048 -max_interleave_delta 0 -flush_packets 0 -fps_mode cfr -f mpegts \
> -y "out.ts"
>
>
> And when the output is analyzed with ffprobe via:
>
> ffprobe -select_streams v -show_entries frame=pict_type,pts_time -of csv=p=0 -skip_frame nokey -i filter.ts > Iframes.txt
>
>
> The GOP distance is clearly set to 10, instead of the specified value of 2:
>
> less Iframes.txt
> 2.981333,I
> 13.221333,I
> 23.461333,I
> 33.701333,I
> 43.941333,I
> 54.181333,I
> 64.421333,I
> 74.661333,I
> 84.901333,I
> 95.141333,I
> 105.381333,I
> 115.621333,I
> 125.861333,I
> 136.101333,I
> 146.341333,I
> 156.581333,I
> 166.821333,I
>
>
> I'll attach the sample file below demonstrating the anomalous GOP size
> issue after encoding.
> Copying in Xiang and Artem.
>
> Warm regards,
>
> Dennis.
>


Hello there,

I fixed it. The root cause of this anomaly is due to the external bit rate
control mode in use (-extbrc 1) which also enables mini-GOPs and scenecut
detection.
Both of these options can be disabled by passing  -adaptive_i 1 -adaptive_b
1