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• Cycle video display ffmpeg

  10 avril 2023, par Lucas McKamey

  I'm new to ffmpeg so I've been struggling to get this code to work so I thought I'd reach out to the community.
Essentially, I was wondering how I could write an ffmpeg command that switches between displaying a video from the inputs I provide every 10 seconds. Ideally, there would be a crossfade transition when switching between videos.
As an example, let's say I have 3 inputs (v1, v2, v3). Say each video is of a duration of 1 minute. The output video would look something like this :

  


  v1(0-10s) -> v2(10-20s) -> v3(20-30s) -> v1(30-40s) -> v2(40-50s) -> v3(50-60s) where the arrows would be crossfade transitions.
Any advice or input you could provide on how I could start on something like this would be a huge help.

  


  Best,
Lucas

  


• probing individual klv streams for specific signature/header

  17 juin 2019, par J Heyman

  Currently, the software I support processes the different streams within a video container (.ts, .mp4, .mpg, etc) without any issues as long as there is only one(1) type of each codec stream.

  I’ve recently encountered a video sample that actually contains three(3) identified AV_CODE_ID_SMPTE_KLV streams. As I loop through the three streams, one of them is the stream I need.
  I haven’t been able to figure out an easy way to do the specific query I need (check for known header bytes in the stream).

      ...
  
      for (i = 0; i < nb_streams; i++) {
  
         int real_stream_index = program ? program[i] : i;
  
         AVStream *st          = ic->streams[real_stream_index];
  
         AVCodecParameters *par = st->codecpar;
  
         if (par->codec_type != type)
  
            continue;
  
         if (id != AV_CODEC_ID_NONE) {
  
            if (par->codec_id != id)
  
               continue;
  
         }
  
         if (wanted_stream_nb >= 0 && real_stream_index != wanted_stream_nb)
  
            continue;
  
         if (type == AVMEDIA_TYPE_AUDIO && !(par->channels && par->sample_rate))
  
            continue;
  
         disposition = !(st->disposition & (AV_DISPOSITION_HEARING_IMPAIRED | AV_DISPOSITION_VISUAL_IMPAIRED));
  
         count = st->codec_info_nb_frames;
  
         bitrate = par->bit_rate;
  
         multiframe = FFMIN(5, count);
  
         if ((best_disposition >  disposition) ||
  
             (best_disposition == disposition && best_multiframe >  multiframe) ||
  
             (best_disposition == disposition && best_multiframe == multiframe && best_bitrate >  bitrate) ||
  
             (best_disposition == disposition && best_multiframe == multiframe && best_bitrate == bitrate && best_count >= count))
  
            continue;
  
         best_disposition = disposition;
  
         best_count   = count;
  
         best_bitrate = bitrate;
  
         best_multiframe = multiframe;
  
         ret          = real_stream_index;

  My thought was to add another || to the complex if{} above, but I haven’t been able to figure out how to do the comparison I need (looking for the header bytes).

  I’ve looked into existing documentation, and thought that accessing the probe_data structure within the AVStream contained within the AVFormatContext structure would give me the first few bytes of the stream. No such luck, as the probe_data structure is empty even though we’ve done a probe on the file itself.

  fprintf(stderr, "Filename: %s\t buf_size: %d\n", st-> probe_data.filename, st-> probe_data.buf_size);

• [C/C++]Converting Jpeg to Motion Jpeg by using FFmpeg

  12 avril 2016, par YJJ

  I’m completely new in this field and trying to convert Jpeg image files to Motion Jpeg Video files by using a FFmpeg Library with C++.

  I made one just using a ffmpeg bat file. but I want to make C++ code lines to do it.

  I thought I have to encode the Jpeg files first, but I saw some references which said I don’t need to encode in this case but just use a mux.

  I am modifying example codes from FFmpeg public page but got really stuck now

  could anyone help me with this please ?