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• How to do precise frame cut with ffmpeg ?

  25 juillet 2020, par Menglun Li

  I tried to cut multiple big videos into many small pieces. I know I can cut and export the small pieces one by one with "Premiere Elements", however that takes a lot time to export them manually. I couldn't find a way to do batch export in "Premiere Elements".

  


  I wrote down the starting and ending points of the small videos from Premiere Elements' timeline viewer, then I created a batch file to use ffmpeg for batch cutting. Below is one of the cutting command in the batch file.

  


  ffmpeg -i input.mp4 -ss 00:20:45.09 -to 00:23:01.00 -c:v libx264 -c:a aac output5.mp4 


  


  I compared the video that was cut by ffmpeg and the video was exported by Premiere Elements. I found sometime they are not starting and ending at the same frame, and it is not consistent either. Both the starting and ending frame that was cut by ffmpeg can drift forward or backward 6-9 frames from the frame number showed in Premiere Elements.

  


  How do I make sure ffmpeg has the precise frame cut ? Thanks in advance.

  


• HLS live stream stops working with AbortError after running fine for a while

  20 juillet 2020, par mandrakey

  Before I go file a bug with Video.js I wanted to see if I maybe have gotten something wrong. The situation is this :

  


  

  • I have a RTSP live stream, which I convert to HLS using ffmpeg (works)

  


  • I want to play that HLS stream using Video.js in the browser

  


  


  After I start ffmpeg, all works as expected and I can watch the live stream in the browser. This was, say, around 4pm. I go home for the day and when I try to access the stream again in the morning (around 8am, freshly started browser) I just get a black image (Firefox) or a still (Chrome) and a never ending loading animation.

  


  The browser console shows the following output every 6 seconds (which is my chunk length) :

  


  AbortError: The operation was aborted. 
XHR GET http://server/hls/live/stream1/720p6.ts [HTTP/1.1 200  71ms]
XHR GET http://server/hls/live/stream1/720p7.ts [HTTP/1.1 200  64ms]
XHR GET http://server/hls/live/stream1/720p8.ts [HTTP/1.1 200  62ms]
XHR GET http://server/hls/live/stream1/720p9.ts [HTTP/1.1 200  57ms]
XHR GET http://server/hls/live/stream1/720p0.ts [HTTP/1.1 200  63ms]


  


  Note : The chunk numbers in the end do change correctly, so it does not look like an infinite loop where video.js tries to access the same files over and over again.

  


  I have compared the m3u8 contents from a time when this happens to just after I restarted ffmpeg. The only difference I can spot is that the sequence number has increased :

  


  Working version

  


  #EXTM3U
#EXT-X-VERSION:3
#EXT-X-TARGETDURATION:6
#EXT-X-MEDIA-SEQUENCE:2
#EXTINF:6.000011,
720p2.ts
#EXTINF:5.999989,
720p3.ts
#EXTINF:6.000000,
720p4.ts
#EXTINF:6.000000,
720p5.ts
#EXTINF:6.000000,
720p6.ts


  


  Not working version

  


  #EXTM3U
#EXT-X-VERSION:3
#EXT-X-TARGETDURATION:6
#EXT-X-MEDIA-SEQUENCE:45255
#EXTINF:6.000011,
720p5.ts
#EXTINF:5.999989,
720p6.ts
#EXTINF:6.000000,
720p7.ts
#EXTINF:6.000011,
720p8.ts
#EXTINF:5.999989,
720p9.ts


  


  What I have confirmed so far :

  


  

  • The video chunks ffmpeg creates work. I have downloaded newly generated chunks and played them using VLC : Got a 6 second video as expected.

  


  • This also means the source stream still works as expected.

  


  • It does not seem to be an issue with the browser as both Firefox and Chrome show the same behaviour.

  


  • When I restart ffmpeg, which as far as I can see only resets the sequence number, everything works fine again after I reload the video.js player.

  


  • It is no one time issue : I have tried this more than 4 days in a row now. Happens every time.

  


  


  Have I stumbled upon a bug in video.js here or am I missing something ?

  


  For reference, this is how I start ffmpeg :

  


  ffmpeg -v info -rtsp_transport tcp -i rtsp://source/stream -c:v copy -c:a copy -hls_time 6 -hls_wrap 10 -start_number 1 /path/to/stream1/720p.m3u8


  


  Thank you very much for reading and taking the time so far. Any help will be much appreciated :)

  


• ffmpeg stops capturing whole hour of HTTP stream after some time

  7 juillet 2020, par CompuChip

  First of all, sorry if I'm using the wrong terminology. I've been playing around with nginx and I'm still a bit confused about RTMP and HLS and other acronyms.

  


  I've managed to setup OBS to stream to an nginx server, which takes the RTMP stream and chops it into pieces for HLS. Here's the relevant part of the nginx configuration file.

  


  rtmp {
    server {
        listen 1935;
        chunk_size 4000;
        ping 30s;
        deny play all;

        application live {
            live on;
            hls on;
            hls_nested on; # Create a new folder for each stream
            hls_path /mnt/hls/live;
            hls_fragment 3s;
            hls_fragment_naming timestamp;
            hls_playlist_length 60s;
        }
    }
}

http {
    server {
        listen 81 ssl;

        #creates the http-location for our full-resolution (desktop) HLS stream - "http://localhost:8080/live/test/index.m3u8"
        location /live {
            # Elided caching and CORS for brevity

            alias /mnt/hls/live;
            add_header Cache-Control no-cache;
            index index.m3u8;
        }
    }
}


  


  This works well, I can view the stream in VLC or on a website and it looks smooth. Now I wanted to add some logging : I'd like to write full hours (starting at xx:00:00 and ending at xx:59:59) to a file named log_yyyymmdd_hh.mp4, e.g. log_20200707_18.mp4 for the files of 7 July 2020, 18:00 - 19:00 hrs. So I've set up an hourly cron job with the following ffmpeg command :

  


  ffmpeg -i https://stream.example.com:81/live/<streamkey> -preset veryfast -maxrate 2000k \&#xA;    -bufsize 2000k -g 60 -t 3600 -y /var/video/log/$(date &#x2B;\%Y\%m\%d_\%H00).mp4 >/dev/null 2>&amp;1&#xA;</streamkey>

  


  At first this seemed to work well, so I left it running happily for about 24 hours. When I checked, most of my hourly files were small ( 100MB) files of about 10 to 15 minutes long. It seems like any small delay in the stream will cause ffmpeg to stop writing to the file. I suspect such hiccups may for example be caused by an OBS plugin and I'll need to look into that, but I would prefer that ffmpeg will retry for some time before giving up. What arguments should I be passing to ffmpeg to make it not break when the stream is down for, say, up to a second every now and then ?.

  


  When I view back the HLS files there don't seem to be any noticeable gaps, so eventually all the data arrives. I went for the crontab solution with ffmpeg because when recording from nginx I could not figure out how to start recording at the start of the whole hour.