When using nvmpi, the nvmpi encoder packet memory pool is empty

[hai-go]

Thank you for sharing. I have successfully compiled ffmpeg containing nvmpi.
But when using it, I found that there was an error prompt, which caused the resulting video to have screen flickering and stuttering, making it unusable. See details below

===== NvVideo: NVENC =====
NvMMLiteBlockCreate : Block : BlockType = 4
875967048
842091865
H264: Profile = 77, Level = 51
Output #0, mp4, to '/home/yzf/media/241fbd906ee0461ea00533d04580ff3c.mp4':
Metadata:
encoder : Lavf61.7.100
Stream #0:0: Audio: aac (LC) (mp4a / 0x6134706D), 24000 Hz, mono, fltp, 69 kb/s
Metadata:
encoder : Lavc61.19.101 aac
Stream #0:1: Video: h264 (avc1 / 0x31637661), yuv420p(tv, bt470bg/bt470bg/smpte170m, progressive), 1080x1440, q=2-31, 2000 kb/s, 30 fps, 15360 tbn
Metadata:
encoder : Lavc61.19.101 h264_nvmpi
NVMEDIA: Need to set EMC bandwidth : 846000
NVMEDIA: Need to set EMC bandwidth : 846000
NvVideo: bBlitMode is set to TRUE
[libnvmpi][W]: EAGAIN. User must read output. nvmpi encoder packet memory pool is empty! Packet will be dropped. There may be artifacts in the output video.
...............
[libnvmpi][W]: EAGAIN. User must read output. nvmpi encoder packet memory pool is empty! Packet will be dropped. There may be artifacts in the output video.
[out#0/mp4 @ 0xaaaaf1321270] video:5169KiB audio:194KiB subtitle:0KiB other streams:0KiB global headers:0KiB muxing overhead: 0.259492%
frame= 663 fps= 48 q=-0.0 Lsize= 5377KiB time=00:00:23.03 bitrate=1912.3kbits/s speed=1.68x
[aac @ 0xaaaaf1324560] Qavg: 342.678

This is the ffmpeg instruction I executed：
./ffmpeg "-i" "/home/yzf/media/411ac54cdea75620a2b428cdc624bfaf.mp3" "-i" "/home/yzf/media/f46e94049f4b4d9ea46753dcb7e6d13b.aac" "-i" "/home/yzf/media/91bd8d1bc4b84a068a835b670162d4b7.mp4" "-i" "/home/yzf/media/4b4e939a83ad47a6b27668a15ff79ac9.mp4" "-i" "/home/yzf/media/f184559b6a284e288cd594b41b6e79fa.mp4" "-filter_complex" "[0:a]volume=18dB[0a];[1:a]volume=4dB[1a];[0a][1a]amix=inputs=2:duration=longest:dropout_transition=2;[2][3]xfade=transition=fade:duration=1:offset=14,format=yuv420p[v3];[v3][4]xfade=transition=wipeleft:duration=1:offset=18,format=yuv420p" "-c:v" "h264_nvmpi" "-c:a" "aac" "/home/yzf/media/241fbd906ee0461ea00533d04580ff3c.mp4"

After testing, it was found that adding xfade=transition=XXX would cause screen distortion and frame loss, while simple video splicing would not cause screen distortion or frame loss. For example: [2:v][3:v][4:v]concat=n=3:v=1

Is there a way to solve it?

[Keylost]

Hi!
The message
"[libnvmpi][W]: EAGAIN. User must read output. nvmpi encoder packet memory pool is empty! Packet will be dropped. There may be artifacts in the output video."
appears when more than 5 (default) encoded packets accumulate in the encoder’s cache, and FFmpeg doesn’t manage to read and send them to the muxer in time, while new packets are already coming in.

This can happen, for example, if the CPU is slow or under heavy load.
You can try increasing the size of this cache, for example like this:
ffmpeg -i <input.mp4> <other arguments> -c:v h264_nvmpi -packet_pool_size:v 32 <other arguments> <output.mp4>
Make sure to pass the -packet_pool_size:v 32 argument after specifying the output video codec.

Also, if your input video files are encoded with H.264 or H.265, I recommend using nvmpi for decoding as well to reduce CPU load.

By default, FFmpeg will select software decoders like libx264 or libx265, which place a high load on the CPU, unlike nvmpi, which uses dedicated hardware blocks.

If your input file is encoded with H.264, you can explicitly specify the decoder before the -i argument like this:
ffmpeg -c:v h264_nvmpi -i <input.mp4> <other arguments> -c:v h264_nvmpi -packet_pool_size:v 32 <other arguments> <output.mp4>