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• I need some help accurately trimming video using the FFmpeg C api

  20 mars 2015, par Justin Bradley

  I need some help accurately trimming video using the FFmpeg C api.
  What I’m seeing is when the input video stream has a time_base of 1/48000 it correctly selects the trimmed start and end times. However when the input video stream has a time_base other than 1/48000 the trim is incorrect.

  Time bases of 1/30000 and 1/24000 trim half the expected video stream length - 10s instead of 20s.
  1/25 trims almost nothing at all - the output file size is only a few kb.

  The audio stream appears to always be trimmed correctly.

  For example if I try to trim the first 20s of a video whose video stream time base is 1/30000, the output mp4’s length is 20s. It has first 10s of video and first 20s of audio.

  I think I’m incorrectly calculating the end_time but I’m not sure why it’s correct for 1/48000 time_base streams.

  record[i].start_time = av_rescale_q((int64_t)( start_time * AV_TIME_BASE ), default_timebase, in_stream->time_base);
  
  record[i].end_time = av_rescale_q((int64_t)( end_time   * AV_TIME_BASE ), default_timebase, in_stream->time_base);

  Here is a more complete sample of code :

  int num_of_streams = ifmt_ctx->nb_streams;
  
  if(num_of_streams > 0) {
  
      // keeps track of each stream's trimmed start and end times
  
      struct stream_pts record[num_of_streams];
  
  
  
      for (i = 0; i < num_of_streams; i++) {
  
          AVStream *in_stream = ifmt_ctx->streams[i];
  
          AVStream *out_stream = avformat_new_stream(ofmt_ctx, in_stream->codec->codec);
  
          if (!out_stream) {
  
              LOGE("=> Failed allocating output stream");
  
              ret = AVERROR_UNKNOWN;
  
              return close_connection(ret);
  
          }
  
  
  
          ret = avcodec_copy_context(out_stream->codec, in_stream->codec);
  
          if (ret < 0) {
  
              LOGE("=> Failed to copy context from input to output stream codec context");
  
              return close_connection(ret);
  
          }
  
          out_stream->codec->codec_tag = 0;
  
          if (ofmt_ctx->oformat->flags & AVFMT_GLOBALHEADER)
  
              out_stream->codec->flags |= CODEC_FLAG_GLOBAL_HEADER;
  
  
  
          AVRational default_timebase;
  
          default_timebase.num = 1;
  
          default_timebase.den = AV_TIME_BASE;
  
  
  
          // determine start/end times for each stream
  
          record[i].index = i;
  
          record[i].start_time = av_rescale_q((int64_t)( start_time * AV_TIME_BASE ), default_timebase, in_stream->time_base);
  
          record[i].end_time = av_rescale_q((int64_t)( end_time   * AV_TIME_BASE ), default_timebase, in_stream->time_base);
  
      }
  
  
  
      av_dump_format(ofmt_ctx, 0, output_file, 1);
  
  
  
      if (!(ofmt->flags & AVFMT_NOFILE)) {
  
          ret = avio_open(&ofmt_ctx->pb, output_file, AVIO_FLAG_WRITE);
  
          if (ret < 0) {
  
              LOGE("=> Could not open output file '%s'", output_file);
  
              return close_connection(ret);
  
          }
  
      }
  
  
  
      ret = avformat_write_header(ofmt_ctx, NULL);
  
      if (ret < 0) {
  
          LOGE("=> Error occurred when opening output file");
  
          return close_connection(ret);
  
      }
  
  
  
      while (1) {
  
          AVStream *in_stream, *out_stream;
  
  
  
          ret = av_read_frame(ifmt_ctx, &pkt);
  
          if (ret < 0)
  
              break;
  
  
  
          in_stream  = ifmt_ctx->streams[pkt.stream_index];
  
          out_stream = ofmt_ctx->streams[pkt.stream_index];
  
  
  
          // copy packet
  
          pkt.pts = av_rescale_q_rnd(pkt.pts, in_stream->time_base, out_stream->time_base, AV_ROUND_NEAR_INF|AV_ROUND_PASS_MINMAX);
  
          pkt.dts = av_rescale_q_rnd(pkt.dts, in_stream->time_base, out_stream->time_base, AV_ROUND_NEAR_INF|AV_ROUND_PASS_MINMAX);
  
          pkt.duration = av_rescale_q(pkt.duration, in_stream->time_base, out_stream->time_base);
  
          pkt.pos = -1;
  
  
  
          // write the frames we're looking for
  
          if(pkt.pts >= record[pkt.stream_index].start_time && pkt.pts <= record[pkt.stream_index].end_time) {
  
              ret = av_interleaved_write_frame(ofmt_ctx, &pkt);
  
              if (ret < 0) {
  
                  LOGE("=> Error muxing packet");
  
                  break;
  
              }
  
          }
  
  
  
          av_free_packet(&pkt);
  
      }
  
  }

• ffmpeg to split mp4 file into segments... after first segment, audio unsynced

  13 avril 2015, par bcsteeve

  I’ve used the ffmpeg command line shown in this question to split MKV files perfectly for a long time. Now i have some MP4 files that i’d like to split and at first it seemed to work, but every subsequent segment after the first has the audio not synced ! And by several seconds.

  I’ve tried forcing keyframes (advice I found on some other sites) and that didn’t help.

  I tried a different program entirely (Avidemux) and it was able to split the file with proper output, but it was a LOT slower, taking upwards of 3 minutes vs less than 2 seconds with ffmpeg. With Avidemux I was able to determine the exact position of the i-frame where I wanted to split, so thinking perhaps that was the syncing problem I tried that exact position (ie. 00:12:17.111 instead of 00:12:16 or whatever) but that didn’t help either.

  Is there an option I’m missing with ffmpeg to get it to properly sync audio to the video when splitting ?

• How to extract the first frame from a video ?

  10 août 2024, par Andrew

  I am trying to extract the first frame from a video to save it as a preview.

  


  Here's an almost working solution using ffmpeg :

  


  func extractFirstFrame(videoBytes []byte) ([]byte, error) {
    input := bytes.NewReader(videoBytes)

    var output bytes.Buffer

    err := ffmpeg.Input("pipe:0").
        Filter("select", ffmpeg.Args{"gte(n,1)"}).
        Output(
            "pipe:1",
            ffmpeg.KwArgs{
                "vframes": 1,
                "format":  "image2",
                "vcodec":  "mjpeg",
            }).
        WithInput(input).
        WithOutput(&output).
        Run()

    if err != nil {
        return nil, fmt.Errorf("error extracting frame: %v", err)
    }

    return output.Bytes(), nil
}


  


  The problem with this is that it can only process horizontal videos. For some reason it will throw a 0xbebbb1b7 error for a vertical videos. I don't understand why is that, probably because this is my very first time with ffmpeg.

  


  Also, I am concerned if this solution is optimal. My assumption is that the whole video will be loaded into the memory first, which is kinda bad and I would like to avoid that

  


  I use https://github.com/u2takey/ffmpeg-go, but errors are the same even if I run it using exec :

  


      cmd := exec.Command(
        "ffmpeg",
        "-i", "pipe:0",
        "-vf", "select=eq(n\\,0)",
        "-q:v", "3",
        "-f", "image2",
        "pipe:1",
    )


  


  Interestingly enough, I noticed that running command in the terminal will work as expected with any type of video ffmpeg -i .\video_2024-08-10_00-03-00.mp4 -vf "select=eq(n\,0)"  -q:v 3 output_image.jpg, so the problem may be on how I send those videos to my server. I useFiber and send videos as multipart/form-data and then read it like this :

  


      form_data, err := c.FormFile("image")
    file, err := form_data.Open()
    bytes, err := io.ReadAll(file)
    ....
    preview, err := extractFirstFrame(bytes)



  


  I also managed to find logs for the failed attempt :

  


  
ffmpeg version 7.0.2-full_build-www.gyan.dev Copyright (c) 2000-2024 the FFmpeg developers
  built with gcc 13.2.0 (Rev5, Built by MSYS2 project)
  configuration: --enable-gpl --enable-version3 --enable-static --disable-w32threads --disable-autodetect --enable-fontconfig --enable-iconv --enable-gnutls --enable-libxml2 --enable-gmp --enable-bzlib --enable-lzma --enable-libsnappy --enable-zlib --enable-librist --enable-libsrt --enable-libssh --enable-libzmq --enable-avisynth --enable-libbluray --enable-libcaca --enable-sdl2 --enable-libaribb24 --enable-libaribcaption --enable-libdav1d --enable-libdavs2 --enable-libuavs3d --enable-libxevd --enable-libzvbi --enable-librav1e --enable-libsvtav1 --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxavs2 --enable-libxeve --enable-libxvid --enable-libaom --enable-libjxl --enable-libopenjpeg --enable-libvpx --enable-mediafoundation --enable-libass --enable-frei0r --enable-libfreetype --enable-libfribidi --enable-libharfbuzz --enable-liblensfun --enable-libvidstab --enable-libvmaf --enable-libzimg --enable-amf --enable-cuda-llvm --enable-cuvid --enable-dxva2 --enable-d3d11va --enable-d3d12va --enable-ffnvcodec --enable-libvpl --enable-nvdec --enable-nvenc --enable-vaapi --enable-libshaderc --enable-vulkan --enable-libplacebo --enable-opencl --enable-libcdio --enable-libgme --enable-libmodplug --enable-libopenmpt --enable-libopencore-amrwb --enable-libmp3lame --enable-libshine --enable-libtheora --enable-libtwolame --enable-libvo-amrwbenc --enable-libcodec2 --enable-libilbc --enable-libgsm --enable-libopencore-amrnb --enable-libopus --enable-libspeex --enable-libvorbis --enable-ladspa --enable-libbs2b --enable-libflite --enable-libmysofa --enable-librubberband --enable-libsoxr --enable-chromaprint
  libavutil      59.  8.100 / 59.  8.100
  libavcodec     61.  3.100 / 61.  3.100
  libavformat    61.  1.100 / 61.  1.100
  libavdevice    61.  1.100 / 61.  1.100
  libavfilter    10.  1.100 / 10.  1.100
  libswscale      8.  1.100 /  8.  1.100
  libswresample   5.  1.100 /  5.  1.100
  libpostproc    58.  1.100 / 58.  1.100
[mov,mp4,m4a,3gp,3g2,mj2 @ 000002a562ff0e80] stream 0, offset 0x30: partial file
[mov,mp4,m4a,3gp,3g2,mj2 @ 000002a562ff0e80] Could not find codec parameters for stream 1 (Video: h264 (avc1 / 0x31637661), none, 720x1280, 3093 kb/s): unspecified pixel format
Consider increasing the value for the 'analyzeduration' (0) and 'probesize' (5000000) options
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'pipe:0':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    creation_time   : 2024-08-09T20:00:29.000000Z
  Duration: 00:00:06.80, start: 0.000000, bitrate: N/A
  Stream #0:0[0x1](eng): Audio: aac (mp4a / 0x6134706D), 22050 Hz, stereo, fltp, 74 kb/s (default)
      Metadata:
        creation_time   : 2024-08-09T20:00:23.000000Z
        handler_name    : SoundHandle
        vendor_id       : [0][0][0][0]
  Stream #0:1[0x2](eng): Video: h264 (avc1 / 0x31637661), none, 720x1280, 3093 kb/s, 30 fps, 30 tbr, 90k tbn (default)
      Metadata:
        creation_time   : 2024-08-09T20:00:23.000000Z
        handler_name    : VideoHandle
        vendor_id       : [0][0][0][0]
Stream mapping:
  Stream #0:1 -> #0:0 (h264 (native) -> mjpeg (native))
[mov,mp4,m4a,3gp,3g2,mj2 @ 000002a562ff0e80] stream 1, offset 0x5d: partial file
[in#0/mov,mp4,m4a,3gp,3g2,mj2 @ 000002a562fda2c0] Error during demuxing: Invalid data found when processing input
Cannot determine format of input 0:1 after EOF
[vf#0:0 @ 000002a5636c0ec0] Task finished with error code: -1094995529 (Invalid data found when processing input)
[vf#0:0 @ 000002a5636c0ec0] Terminating thread with return code -1094995529 (Invalid data found when processing input)
[vost#0:0/mjpeg @ 000002a5636c0400] Could not open encoder before EOF
[vost#0:0/mjpeg @ 000002a5636c0400] Task finished with error code: -22 (Invalid argument)
[vost#0:0/mjpeg @ 000002a5636c0400] Terminating thread with return code -22 (Invalid argument)
[out#0/image2 @ 000002a562ff5640] Nothing was written into output file, because at least one of its streams received no packets.
frame=    0 fps=0.0 q=0.0 Lsize=       0KiB time=N/A bitrate=N/A speed=N/A
Conversion failed!


  


  Logs for the same video, but ran via terminal :

  


  ffmpeg version 7.0.2-full_build-www.gyan.dev Copyright (c) 2000-2024 the FFmpeg developers
  built with gcc 13.2.0 (Rev5, Built by MSYS2 project)
  configuration: --enable-gpl --enable-version3 --enable-static --disable-w32threads --disable-autodetect --enable-fontconfig --enable-iconv --enable-gnutls --enable-libxml2 --enable-gmp --enable-bzlib --enable-lzma --enable-libsnappy --enable-zlib --enable-librist --enable-libsrt --enable-libssh --enable-libzmq --enable-avisynth --enable-libbluray --enable-libcaca --enable-sdl2 --enable-libaribb24 --enable-libaribcaption --enable-libdav1d --enable-libdavs2 --enable-libuavs3d --enable-libxevd --enable-libzvbi --enable-librav1e --enable-libsvtav1 --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxavs2 --enable-libxeve --enable-libxvid --enable-libaom --enable-libjxl --enable-libopenjpeg --enable-libvpx --enable-mediafoundation --enable-libass --enable-frei0r --enable-libfreetype --enable-libfribidi --enable-libharfbuzz --enable-liblensfun --enable-libvidstab --enable-libvmaf --enable-libzimg --enable-amf --enable-cuda-llvm --enable-cuvid --enable-dxva2 --enable-d3d11va --enable-d3d12va --enable-ffnvcodec --enable-libvpl --enable-nvdec --enable-nvenc --enable-vaapi --enable-libshaderc --enable-vulkan --enable-libplacebo --enable-opencl --enable-libcdio --enable-libgme --enable-libmodplug --enable-libopenmpt --enable-libopencore-amrwb --enable-libmp3lame --enable-libshine --enable-libtheora --enable-libtwolame --enable-libvo-amrwbenc --enable-libcodec2 --enable-libilbc --enable-libgsm --enable-libopencore-amrnb --enable-libopus --enable-libspeex --enable-libvorbis --enable-ladspa --enable-libbs2b --enable-libflite --enable-libmysofa --enable-librubberband --enable-libsoxr --enable-chromaprint
  libavutil      59.  8.100 / 59.  8.100
  libavcodec     61.  3.100 / 61.  3.100
  libavformat    61.  1.100 / 61.  1.100
  libavdevice    61.  1.100 / 61.  1.100
  libavfilter    10.  1.100 / 10.  1.100
  libswscale      8.  1.100 /  8.  1.100
  libswresample   5.  1.100 /  5.  1.100
  libpostproc    58.  1.100 / 58.  1.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '.\video_2024-08-10_00-03-00.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    creation_time   : 2024-08-09T20:00:29.000000Z
  Duration: 00:00:06.80, start: 0.000000, bitrate: 3175 kb/s
  Stream #0:0[0x1](eng): Audio: aac (HE-AAC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 74 kb/s (default)
      Metadata:
        creation_time   : 2024-08-09T20:00:23.000000Z
        handler_name    : SoundHandle
        vendor_id       : [0][0][0][0]
  Stream #0:1[0x2](eng): Video: h264 (Baseline) (avc1 / 0x31637661), yuv420p(tv, bt709, progressive), 720x1280, 3093 kb/s, 30 fps, 30 tbr, 90k tbn (default)
      Metadata:
        creation_time   : 2024-08-09T20:00:23.000000Z
        handler_name    : VideoHandle
        vendor_id       : [0][0][0][0]
Stream mapping:
  Stream #0:1 -> #0:0 (h264 (native) -> mjpeg (native))
Press [q] to stop, [?] for help
[swscaler @ 00000219eb4d0c00] deprecated pixel format used, make sure you did set range correctly
Output #0, image2, to 'output_image.jpg':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf61.1.100
  Stream #0:0(eng): Video: mjpeg, yuvj420p(pc, unknown/bt709/bt709, progressive), 720x1280, q=2-31, 200 kb/s, 30 fps, 30 tbn (default)
      Metadata:
        creation_time   : 2024-08-09T20:00:23.000000Z
        handler_name    : VideoHandle
        vendor_id       : [0][0][0][0]
        encoder         : Lavc61.3.100 mjpeg
      Side data:
        cpb: bitrate max/min/avg: 0/0/200000 buffer size: 0 vbv_delay: N/A
[image2 @ 00000219e7aa51c0] The specified filename 'output_image.jpg' does not contain an image sequence pattern or a pattern is invalid.
[image2 @ 00000219e7aa51c0] Use a pattern such as %03d for an image sequence or use the -update option (with -frames:v 1 if needed) to write a single image.
[out#0/image2 @ 00000219e7b5e400] video:49KiB audio:0KiB subtitle:0KiB other streams:0KiB global headers:0KiB muxing overhead: unknown
frame=    1 fps=0.0 q=3.0 Lsize=N/A time=00:00:00.03 bitrate=N/A speed=0.322x


  


  I also realized that the problem was not related to the video orientation, but to to the video from a specific source uploaded specifically on my server 🤡 Such a weird coincidence that I decided to test my video upload with those files, but anyway. And those are.... Downloaded instagram reels lol. But again, ffmpeg works just fine when ran in terminal