On the state of FFmpeg's ffv1_vulkan encoder implementation on Intel & NVIDIA

[Dennis E. Mungai]

The subject matter above refers.
Sample command-lines are provided for reference, see the notes section below.

(a). Intel:

ffmpeg \
-init_hw_device vulkan=vk:0 \
-hwaccel vulkan -hwaccel_output_format vulkan \
-hwaccel_device vk -filter_hw_device vk \
-loglevel info \
-fflags +genpts \
-i '4KIOS.mov' \
-vf "bwdif_vulkan,libplacebo=format=yuv420p" \
-c:v ffv1_vulkan \
-r:v 60 -g:v 2 -level:v 4 -strict -2 -coder:v 2 -context:v 1 \
-c:a libfdk_aac -b:a 128k -ar 48000 -ac 2 \
-map "0:v" -map "0:a" \
-max_muxing_queue_size 8192 -max_interleave_delta 0 \
-flags -global_header+cgop \
-y -f matroska "ticketx_ffv1.mkv"

(b). NVIDIA:

ffmpeg \
-init_hw_device vulkan=vk:0 \
-hwaccel vulkan -hwaccel_output_format vulkan \
-hwaccel_device vk -filter_hw_device vk \
-loglevel info \
-fflags +genpts \
-i '4KIOS.mov' \
-vf "bwdif_vulkan,libplacebo=format=yuv420p" \
-c:v ffv1_vulkan \
-r:v 60 -g:v 2 -level:v 4 -strict -2 -coder:v 2 -context:v 1 \
-c:a libfdk_aac -b:a 128k -ar 48000 -ac 2 \
-map "0:v" -map "0:a" \
-max_delay 5000000 -max_muxing_queue_size 8192 -max_interleave_delta 0 \
-flags -global_header+cgop \
-y -f matroska "ticket4_ffv1.mkv"

Runtime notes:

It's observed that the encoder also works quite well with and without using Vulkan H/W Accelerated decode, producing consistent results across multiple runs per test platform with and without Vulkan H/W Accelerated decode.

As noted by Lynne on IRC regarding this encoder, handling yuv420p requires the following conditions to be met:

1. Either 64 pixel aligned images for both h and v.
2. And using version 4 (Pass -level 4 -strict -2).

The example commands above have the flags -strict -2 and -level:v 4 set to match the constraints defined above.

Oddities/bugs:

1. Even with identical parameters, the file sizes produced by Intel's and NVIDIA's ffv1_vulkan instances differ significantly.

Intel's anv driver produces ridiculously massive files as shown below:
The file from NVIDIA's session,named "ticket4_ffv1.mkv" is about 4.9G in size.
Intel's session output with the same settings, named "ticketx_ffv1.mkv", weighs at 41 GB.

2. NVIDIA's performance with this encoder, as tested on the RTX 4060 Max Q with a 4k input sample is at about ~0.63x speed.

Intel's performance on the Integrated Raptor Lake GPU with the ANV driver clocks in at a paltry speed of 0.0907x. 7x slower.

3. With NVIDIA, the ffv1_vulkan encoder will hang at a sporadic frame on each session *if* -g:v is higher than 2, regardless of the -level:v setting, all else being constant.