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• FFMPEG stereo track stops capturing at random times during a capture session

  26 mai 2022, par mrwassen

  I am currently working on building a workflow to capture and archive a large stash of family and friends PAL and NTSC VHS tapes. The hardware setup is as follows :

  


  

  • JVC HR-7860S VCR

  


  • s-video / RCA audio >

  


  • ADVC-3000 converter

  


  • SDI / BNC cable >

  


  • Blackmagic Decklink Mini Recorder 4K PCIe card

  


  • installed in a fairly hi-spec windows machine : AMD Ryzen 9 5900X 3.7 Ghz base 12 core, GEFORCE RTX 3060 12 gB, 32 gB ram

  


  


  The plan is to capture to lossless AVI, then drop into an NLE (Vegas Pro v.16) to do a minimal amount of cleanup / trimming, then render to a more compressed video format (TBD) for upload to AWS S3 accessible through a family website.

  


  The issue I am having is that when I run the capture using ffmpeg/directshow e.g. for a perfectly fine 90 min. PAL tape, at some random point of time during the capture one of the 2 stereo channels just stops capturing. This has happened with all of the tapes I have tested so far, and it happens at different times during the same video. I have examined the frames surrounding points in time when this happens, and it doesn't correlate to any transitions or jitter, but often just randomly in the middle of a perfectly smooth scene. Once the one channel stops capturing it never starts back up again during that capture session.

  


  The ADVC-3000 and the VCR are both showing both stereo channels playing normally throughout the capture. The windows machine running the capture hardly breaks a sweat at any time, and the transfer easily keeps up constantly showing a speed = 1x which I assume means nothing lagging. Also there are no video/audio sync issues at any point in time even towards the end of long tapes e.g. 90 mins.

  


  I am fairly new at ffmpeg, so I have spent extensive amounts of time reading up on forum posts and experimenting and have ended up with the following syntax :

  


  ffmpeg -y -f dshow -rtbufsize 2000M -i video="Blackmagic WDM Capture":audio="Blackmagic WDM Capture" -codec:v v210 -pix_fmt yuv422p -codec:a pcm_s16le -b:a 128k -t 02:00:00 -r 25 -threads 4 -maxrate 2500k -filter:a "volume=1.5" output_v210_audio.avi


  


  The capture runs without a single dropped frame, the only error I am getting when launching (and perhaps this is a smoking gun ?) is :

  


  


  "Non-monotonous DTS in output stream 0:1 ; previous : 0, current : -30 ;
changing to 1. This may result in incorrect timestamps in the output
file."

  


  


  I have tried to troubleshoot this in the hopes that it is tied to my issue but so far without luck.

  


  Hoping somebody can help correct or modify my command line or perhaps other ideas to help resolve the issue.

  


• Heroku FFMPEG HEVC Video with Alpha support ?

  15 septembre 2022, par Patrick Vellia

  I am looking for a way to handle converting videos like Webm VP9 with alpha channel to HEVC with alpha mov or mp4 files that are playable in Safari (The Webm will work in all other browsers).

  


  While I can do this locally in my Rails app using streamio-ffmpeg gem and the havoc_videotoolbox encoder, this only works on Apple hardware.

  


  Therefore if I push it up to Heroku and use the Heroku ffmpeg build pack, the HEVC VideoToolbox is not available for use.

  


  FFMPEG does have the libx265 encoder but I can't find the property for this one to preserve the alpha channel.

  


  ffmpeg -I INPUT -c:v libx265 -preset medium -crf 26 -tag:v hvc1 OUTput.mp4


  


  there is a -x265-params flag, but I can't figure out which param will enable the alpha channel.

  


  I am hoping this is actually possible for my production app, otherwise I'd have to process this segment of our media locally and manually upload the HEVC components.

  


  Local Configuration
Apple Monterey with ffmpeg 5.1.1 installed on Intel
Rails 7

  


  Heroku

  


  FFMPEG build pack

  


  Hobby Plan

  


  Rails 7

  


• Create drawbox with ffmpeg between specific seconds (without reencoding whole video - faster)

  31 mars 2022, par protter

  My plan was to put a transparent red box behind a video. This box should only be present from second 1-45.
But if the videos are 3 hours long, the process takes a long time although it only has to process 45 seconds.

  


  My first attempt takes too long :

  


  ffmpeg -i %1 -vf drawbox=0:9*ih/10:iw:ih/10:t=fill:color=red@0.5:enable='between(t,1,45)' "%~dp0transpred\%~n1%~x1

  


  Then i tried splitting the video into two parts. put the box on the first video, and then put the two back together again.

  


  ffmpeg  -ss 00:00:00.0000 -i %1 -to 00:00:45.0000  -vf drawbox=0:9*ih/10:iw:ih/10:t=fill:color=red@0.5:enable='between(t,1,45)' "%~dp0transpred\%~n1A%~x1"

  


  FFMpeg -ss 00:00:45.0000 -i %1 -c:v copy -c:a copy -avoid_negative_ts make_zero "%~dp0transpred\%~n1B%~x1"

  


  But i don't even have to try to put these two together, because they are not separated exactly at the second. I have read that this is due to "timestamps" and the different video and audio streams.

  


  Now I'm trying an approach to create a stream with the bar, and then overlay it with the finished video. I haven't quite managed that yet, and I don't know if it's faster.
Shortening the video is very fast.

  


  EDIT (Added as a replacement for the comment later)

  


  Thanks for your help I have almost done it with a slightly different approach. Unfortunately, the second part now always has no sound. No matter if I put A and B (B no sound) or B and A (A no sound) together.

  


  

  1. First split with mkvmerge so i have no worrys about the keyframes and get the exact time
mkvmerge --split timestamps:00:00:45.100 A.MKV -o splitmkm.mkv

  


  2. Then add the Bar (Black because of easier testing) :
ffmpeg -i splitmkm-001.mkv -vf drawbox=0:9*ih/10:iw:ih/10:t=fill BAR1.MKV

  


  3. Merge (mkvmerge ends with error) :
ffmpeg -safe 0 -f concat -i list.txt -c copy output1.mkv

  


  


  EDIT (Answer to kesh)

  


  This was the error Again, audio codec config's must match across all your concat files. The drawbox changed the audio Codec from AC-3 to Vorbis.

  


  the procedure is now :

  


  

  1. mkvtoolnix\mkvmerge --split timestamps:00:00:05.100  %1 -o A_splitmkm.mkv with mkvmerge i have an exact split at the time, and i don't have to learn about keyframes.

  


  2. ffmpeg -i A_splitmkm-001.mkv -vf drawbox=0:9*ih/10:iw:ih/10:t=fill:color=red A_BARmkm.MKV create the Bar

  


  3. ffmpeg -i A_BARmkm.MKV -i A_splitmkm-001.mkv -map 0:v  -map 1 -map -1:v  -c copy A_BARwithAudio.mkv redo the step with the changed audio from drawbox

  


  4. ffmpeg -safe 0 -f concat -i list.txt -map 0  -c copy A_output1.mkv merge

  


  


  Now everything works.
Thanks alot !