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• ffmpeg how to convert audio to aac but keep bit rate at what the old file used ?

  3 novembre 2017, par gregm

  I don’t expect this to happen often, but while re-encoding video files via batch file to h265 I’m checking to make sure the audio is in aac. If it isn’t then I want to convert to aac, but keep the bit rate at what ever the old file uses since if I just convert to aac ffmpeg is going to use the default 128kbps value. For any old videos I have the bit rate is probably going to be lower than that so upconverting is going to increase the file size a little.

  Is there any way to convert to aac but keep the old bit rate ?

  Here’s what I was trying but it keeps converting the old mp3 89kbps stream to aac 128 kbps :

  ffmpeg -i test.mp4 -acodec aac -vcodec copy test.aac.mp4

  Note that above is just for test purposes, I am actually converting the video.

  Note 2 : My question isn’t at all similar to the other question that it has been suggested as similar to. I have no trouble storing ffprobe results in variables nor did I even mention that.

• Using FFMPEG libs to UDP stream mpeg2 ts video delay / initial connection problems

  16 mars 2015, par ccoral

  Currently using the lib’s from FFPMEG to stream some MPEG2 TS (h264 encoded) video. The streaming is done via UDP multicast.

  The issue I am having currently is two main things. There is a long initial connection time / getting the video to show (the stream also contains metadata, and that stream is detected by my media tool immediately).

  Once the video gets going things are fine but it is always delayed by that initial connection time.

  I am trying to get as near to LIVE streaming as possible.

  Currently using the av_dict_set(&dict, "tune", "zerolatency", 0) and "profile" -> "baseline" options.

  GOP size = 12 ;

  At first I thought the issue was an i frame issue, but the initial delay is there if gopsize is 12 or default 250. Sometimes the video will connect quickly, but it is immediately dropped, the delay occurs, then it starts back up and is good from that point on.

  According to documentation the zero latency option should be sending many i frames, to limit initial syncing delays.

  I am starting to think its a buffering type issue, as when I close the application and leave the media player up, it then fast forwards through the delay till it hits basically where the file stops streaming.

• ffmpeg, how to extract single frame, 0.5 seconds before the end ? [duplicate]

  24 avril 2020, par Tonny

  I've got a bunch (several 100) of videos (all different frame-rates and different lengths).
  
Each has an end-title during the last second of the video, that shows some important information I need to check.
  
Playing each video in a player, scrolling to the end and trying to pause it in the last second is just to cumbersome/time-consuming.
  
Grabbing a frame at that position and saving it as an image for each video lets me quickly check the info using the image-preview in my file-manager. Which is much more efficient.

  



  ffmpeg can capture single frames and write them to a jpg or png, but I am at a loss how to extract a frame in the middle of that title sequence. 0.5 seconds before the end of each video would be the sweet spot. (There is a animation effect during that 1 second sequence that makes the text in the video sometimes hard to read, but exactly in the middle the visibility is best.)
  
As far as I can tell ffmpeg can't use offsets "from the end", so I assume ffprobe is probably needed to analyze the video and on basis off that the correct ffmpeg command can be generated.

  



  I can handle the scripting around it to batch-process all the files.
  
Problem is that I'm very unfamiliar with video in general, ffmpeg and ffprobe in particular. I need some help to get started.
  
If someone can explain to me how to get from the full video 'clip.mp4' to the single frame 0.5 seconds before the end in 'clip_frame.jpg' I would be most grateful.