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FFmpeg RTSP drop rate increases when frame rate is reduced
13 avril 2024, par Avishka PereraI need to read an RTSP stream, process the images individually in Python, and then write the images back to an RTSP stream. As the RTSP server, I am using Mediamtx [1]. For streaming, I am using FFmpeg [2].


I have the following code that works perfectly fine. For simplification purposes, I am streaming three generated images.


import time
import numpy as np
import subprocess

width, height = 640, 480
fps = 25
rtsp_server_address = f"rtsp://localhost:8554/mystream"

ffmpeg_cmd = [
 "ffmpeg",
 "-re",
 "-f",
 "rawvideo",
 "-pix_fmt",
 "rgb24",
 "-s",
 f"{width}x{height}",
 "-i",
 "-",
 "-r",
 str(fps),
 "-avoid_negative_ts",
 "make_zero",
 "-vcodec",
 "libx264",
 "-threads",
 "4",
 "-f",
 "rtsp",
 rtsp_server_address,
]
colors = np.array(
 [
 [255, 0, 0],
 [0, 255, 0],
 [0, 0, 255],
 ]
).reshape(3, 1, 1, 3)
images = (np.ones((3, width, height, 3)) * colors).astype(np.uint8)

if __name__ == "__main__":

 process = subprocess.Popen(ffmpeg_cmd, stdin=subprocess.PIPE)
 start = time.time()
 exported = 0
 while True:
 exported += 1
 next_time = start + exported / fps
 now = time.time()
 if next_time > now:
 sleep_dur = next_time - now
 time.sleep(sleep_dur)

 image = images[exported % 3]
 image_bytes = image.tobytes()

 process.stdin.write(image_bytes)
 process.stdin.flush()

 process.stdin.close()
 process.wait()



The issue is, that I need to run this at 10 fps because the processing step is heavy and can only afford 10 fps. Hence, as I reduce the frame rate from 25 to 10, the drop rate increases from 0% to 100%. And after a few iterations, I get a
BrokenPipeError: [Errno 32] Broken pipe
. Refer to the appendix for the complete log.

As an alternative, I can use OpenCV compiled from source with GStreamer [3], but I prefer using FFmpeg to make the shipping process simple. Since compiling OpenCV from source can be tedious and dependent on the system.


References


[1] Mediamtx (formerly rtsp-simple-server) : https://github.com/bluenviron/mediamtx


[2] FFmpeg : https://github.com/FFmpeg/FFmpeg


[3] Compile OpenCV with GStreamer : https://github.com/bluenviron/mediamtx?tab=readme-ov-file#opencv


Appendix


Creating the source stream


To instantiate the unprocessed stream, I use the following command. This streams the content of my webcam as and RTSP stream.


ffmpeg -video_size 1280x720 -i /dev/video0 -avoid_negative_ts make_zero -vcodec libx264 -r 10 -f rtsp rtsp://localhost:8554/webcam



Error log


ffmpeg version 6.1.1 Copyright (c) 2000-2023 the FFmpeg developers
 built with gcc 12.3.0 (conda-forge gcc 12.3.0-5)
 configuration: --prefix=/home/conda/feedstock_root/build_artifacts/ffmpeg_1712656518955/_h_env_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_plac --cc=/home/conda/feedstock_root/build_artifacts/ffmpeg_1712656518955/_build_env/bin/x86_64-conda-linux-gnu-cc --cxx=/home/conda/feedstock_root/build_artifacts/ffmpeg_1712656518955/_build_env/bin/x86_64-conda-linux-gnu-c++ --nm=/home/conda/feedstock_root/build_artifacts/ffmpeg_1712656518955/_build_env/bin/x86_64-conda-linux-gnu-nm --ar=/home/conda/feedstock_root/build_artifacts/ffmpeg_1712656518955/_build_env/bin/x86_64-conda-linux-gnu-ar --disable-doc --disable-openssl --enable-demuxer=dash --enable-hardcoded-tables --enable-libfreetype --enable-libharfbuzz --enable-libfontconfig --enable-libopenh264 --enable-libdav1d --enable-gnutls --enable-libmp3lame --enable-libvpx --enable-libass --enable-pthreads --enable-vaapi --enable-libopenvino --enable-gpl --enable-libx264 --enable-libx265 --enable-libaom --enable-libsvtav1 --enable-libxml2 --enable-pic --enable-shared --disable-static --enable-version3 --enable-zlib --enable-libopus --pkg-config=/home/conda/feedstock_root/build_artifacts/ffmpeg_1712656518955/_build_env/bin/pkg-config
 libavutil 58. 29.100 / 58. 29.100
 libavcodec 60. 31.102 / 60. 31.102
 libavformat 60. 16.100 / 60. 16.100
 libavdevice 60. 3.100 / 60. 3.100
 libavfilter 9. 12.100 / 9. 12.100
 libswscale 7. 5.100 / 7. 5.100
 libswresample 4. 12.100 / 4. 12.100
 libpostproc 57. 3.100 / 57. 3.100
Input #0, rawvideo, from 'fd:':
 Duration: N/A, start: 0.000000, bitrate: 184320 kb/s
 Stream #0:0: Video: rawvideo (RGB[24] / 0x18424752), rgb24, 640x480, 184320 kb/s, 25 tbr, 25 tbn
Stream mapping:
 Stream #0:0 -> #0:0 (rawvideo (native) -> h264 (libx264))
[libx264 @ 0x5e2ef8b01340] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX FMA3 BMI2 AVX2
[libx264 @ 0x5e2ef8b01340] profile High 4:4:4 Predictive, level 2.2, 4:4:4, 8-bit
[libx264 @ 0x5e2ef8b01340] 264 - core 164 r3095 baee400 - H.264/MPEG-4 AVC codec - Copyleft 2003-2022 - http://www.videolan.org/x264.html - options: cabac=1 ref=3 deblock=1:0:0 analyse=0x3:0x113 me=hex subme=7 psy=1 psy_rd=1.00:0.00 mixed_ref=1 me_range=16 chroma_me=1 trellis=1 8x8dct=1 cqm=0 deadzone=21,11 fast_pskip=1 chroma_qp_offset=4 threads=4 lookahead_threads=1 sliced_threads=0 nr=0 decimate=1 interlaced=0 bluray_compat=0 constrained_intra=0 bframes=3 b_pyramid=2 b_adapt=1 b_bias=0 direct=1 weightb=1 open_gop=0 weightp=2 keyint=250 keyint_min=10 scenecut=40 intra_refresh=0 rc_lookahead=40 rc=crf mbtree=1 crf=23.0 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.40 aq=1:1.00
Output #0, rtsp, to 'rtsp://localhost:8554/mystream':
 Metadata:
 encoder : Lavf60.16.100
 Stream #0:0: Video: h264, yuv444p(tv, progressive), 640x480, q=2-31, 10 fps, 90k tbn
 Metadata:
 encoder : Lavc60.31.102 libx264
 Side data:
 cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: N/A
[vost#0:0/libx264 @ 0x5e2ef8b01080] Error submitting a packet to the muxer: Broken pipe 
[out#0/rtsp @ 0x5e2ef8afd780] Error muxing a packet
[out#0/rtsp @ 0x5e2ef8afd780] video:1kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown
frame= 1 fps=0.1 q=-1.0 Lsize=N/A time=00:00:04.70 bitrate=N/A dup=0 drop=70 speed=0.389x 
[libx264 @ 0x5e2ef8b01340] frame I:16 Avg QP: 6.00 size: 147
[libx264 @ 0x5e2ef8b01340] frame P:17 Avg QP: 9.94 size: 101
[libx264 @ 0x5e2ef8b01340] frame B:17 Avg QP: 9.94 size: 64
[libx264 @ 0x5e2ef8b01340] consecutive B-frames: 50.0% 0.0% 42.0% 8.0%
[libx264 @ 0x5e2ef8b01340] mb I I16..4: 81.3% 18.7% 0.0%
[libx264 @ 0x5e2ef8b01340] mb P I16..4: 52.9% 0.0% 0.0% P16..4: 0.0% 0.0% 0.0% 0.0% 0.0% skip:47.1%
[libx264 @ 0x5e2ef8b01340] mb B I16..4: 0.0% 5.9% 0.0% B16..8: 0.1% 0.0% 0.0% direct: 0.0% skip:94.0% L0:56.2% L1:43.8% BI: 0.0%
[libx264 @ 0x5e2ef8b01340] 8x8 transform intra:15.4% inter:100.0%
[libx264 @ 0x5e2ef8b01340] coded y,u,v intra: 0.0% 0.0% 0.0% inter: 0.0% 0.0% 0.0%
[libx264 @ 0x5e2ef8b01340] i16 v,h,dc,p: 97% 0% 3% 0%
[libx264 @ 0x5e2ef8b01340] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 0% 0% 100% 0% 0% 0% 0% 0% 0%
[libx264 @ 0x5e2ef8b01340] Weighted P-Frames: Y:52.9% UV:52.9%
[libx264 @ 0x5e2ef8b01340] ref P L0: 88.9% 0.0% 0.0% 11.1%
[libx264 @ 0x5e2ef8b01340] kb/s:8.27
Conversion failed!
Traceback (most recent call last):
 File "/home/avishka/projects/read-process-stream/minimal-ffmpeg-error.py", line 58, in <module>
 process.stdin.write(image_bytes)
BrokenPipeError: [Errno 32] Broken pipe
</module>


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