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• Use ffmpeg to record from RTSP stream to two outputs at different resolutions while segmenting the video based on time

  7 juin 2023, par Eric Hansen

  I need to record from an RTSP at two different resolutions (original and something lower). I also need to have the files broken up according to clock time on every even 30 minutes, ex. 1:00, 1:30, 2:00, etc.

  


  I imagine the command would look like this.

  


  ffmpeg -rtsp_transport tcp -i rtsp://<rtsp url="url"> \&#xA;  -filter_complex "[0:v]split=2[v1][v2];[v1]scale=1920:1080[out1];[v2]scale=448:252[out2]" \&#xA;  -map "[out1]" -c:v -f segment -segment_format mp4 -segment_time 00:30:00 -strftime 1 \ &#xA;  /mnt/data/original-%Y-%m-%d-%H.%M.%S.mp4 \&#xA;  -map "[out2]" -c:v -f segment -segment_format mp4 -segment_time 00:30:00 -strftime 1 \ &#xA;  /mnt/data/low-reso-%Y-%m-%d-%H.%M.%S.mp4 \&#xA;</rtsp>

  


  Of course, this doesn't work. The command above gives me this error.

  


  [NULL @ 0x556c999c2140] Unable to find a suitable output format for 'segment'
segment: Invalid argument


  


  I've tried so many perturbations of this command to get it to work without any luck. Does anyone know how to do this ?

  


• Sync audio from microphone and video from camera, saved in seperate files, using ffmpeg

  20 octobre 2023, par Lucas

  I am grabbing frames coming up from my camera using a pipe and simultaneously the audio coming from a microphone.

  


  I would like to have the audio and video in seperated files but precisely synchronized.

  


  I have tried to set the pts of both stream using the internal computer clock by setting the use_wallclock_as_timestamps option.

  


  But when I take a look into the duration of both video and audio using mediainfo, the duration has a delay of 10 to 100 ms between them.

  


  Here is the code I used so far :

  


  ffmpeg -y //
-f rawvideo -pixel_format bgr24 -video_size 2048x1088 -use_wallclock_as_timestamps 1 -i - //
-f alsa -ac 2 -use_wallclock_as_timestamps 1 -i sysdefault:CARD=H4 //
-map 0 -c:v mpeg4 -qscale:v 1 -vf "setpts=PTS-STARTPTS" -fps_mode cfr -r 50 Camera.avi //
-map 1 Audio.wav 


  


  when running this command ffmpeg prompts that the starting time of the video stream is ahead of the audio, resulting to a delay. Unfortunately this delay does not correspond to the total delay
I get at the end.

  


  I am running on linux 20.04.

  


• FFMPEG generated h264/aac mp4 video first frame doesn't report a zero mediaTime using requestVideoFrameCallback html api [closed]

  12 mai 2023, par Daniel Robinson

  I have noticed that mp4 files generated using ffmpeg aren’t reporting a mediaTime of 0 via requestVideoFrameCallback for the first frame however files encoded as webm or via another encoder such as mainconcept its 0.

  


  You can see a demo of the issue here https://randomstuffdr.s3.eu-west-1.amazonaws.com/TEST-v3.HTML
As you increment the frames with video 1 you don’t see video progress until the third button press.

  


  With video 2-4, the mediaTime is 0 and a single press of the button increments the video by one frame.

  


  Browser : Chrome 113.0.5672.92 (Windows 10)

  


  FFMPEG Version : 6.0-essentials_build-www.gyan.dev or N-109421-g9adf02247c-20221216

  


  There was an interesting note on this page related to mediaTime implementation in chrome https://web.dev/requestvideoframecallback-rvfc/

  


  


  Of special interest in this list is mediaTime. In Chromium's
implementation, we use the audio clock as the time source that backs
video.currentTime, whereas the mediaTime is directly populated by the
presentationTimestamp of the frame. The mediaTime is what you should
use if you want to exactly identify frames in a reproducible way,
including to identify exactly which frames you missed.

  


  


  The led me to compare the PTS files of the video and audio stream between the ffmpeg and MC files using ffprobe however these are all zero for the first frames. The one interesting note, is that ffmpeg file seems to interleave video and audio packets in ffprobe while the mainconcept file has 8 video frames before audio, I have no idea if this is significant.

  


  What I would like to know is if there is any way I can make ffmpeg generate a file in a similar manner to mainconcept ? So far I have tried ; disabling b-frames, use baseline profile and avoid_negative_ts

  


  Video 1 – (Video : H264 /Audio : AAC / Wrapper : MP4 / Transcoder : FFMPEG)
.\ffmpeg.exe -i '720p50 Flash and Beep.mxf' -map 0:0 -map 0:1 -map_metadata -1 -c:v libx264 -crf 28 -b:v 118k -maxrate 118k -bufsize 236k -vf scale="480 :-1" -preset veryfast -c:a aac "..\low-res\720p50FlashandBeep_V_A.mp4"

  


  Video 2 – (Video : H264 /Audio : No Audio / Wrapper : MP4 / Transcoder : FFMPEG)
.\ffmpeg.exe -i '720p50 Flash and Beep.mxf' -map 0:0 -map 0:1 -map_metadata -1 -c:v libx264 -crf 28 -b:v 118k -maxrate 118k -bufsize 236k -vf scale="480 :-1" -preset veryfast -an "..\low-res\720p50FlashandBeep_V.mp4"

  


  Video 3 – (Video : vp8 /Audio : ogg / Wrapper : webm / Transcoder : FFMPEG)
.\ffmpeg.exe -i '720p50 Flash and Beep.mxf' -map 0:0 -map 0:1 -map_metadata -1 -c:v vp8 -crf 28 -b:v 118k -maxrate 118k -bufsize 236k -vf scale="480 :-1" -preset veryfast "..\low-res\720p50FlashandBeep_V_A.webm"

  


  Video 4 – (Video : H264 /Audio : AAC / Wrapper : MP4 / Transcoder : MainConcept)