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• Cutting MPEG-TS file via ffmpegwrapper ?

  27 janvier 2016, par Stefan Kendall

  I have MPEG-TS files on the device. I would like to cut a fairly-exact time off the start of the files on-device.

  Using FFmpegWrapper as a base, I’m hoping to achieve this.

  I’m a little lost on the C API of ffmpeg, however. Where do I start ?

  I tried just dropping all packets prior to a start PTS I was looking for, but this broke the video stream.

      packet->pts = av_rescale_q(packet->pts, inputStream.stream->time_base, outputStream.stream->time_base);
  
      packet->dts = av_rescale_q(packet->dts, inputStream.stream->time_base, outputStream.stream->time_base);
  
  
  
      if(startPts == 0){
  
          startPts = packet->pts;
  
      }
  
  
  
      if(packet->pts < cutTimeStartPts + startPts){
  
          av_free_packet(packet);
  
          continue;
  
      }

  How do I cut off part of the start of the input file without destroying the video stream ? When played back to back, I want 2 cut segments to run seamlessly together.

  ffmpeg -i time.ts -c:v libx264 -c:a copy -ss $CUT_POINT -map 0 -y after.ts
  
  ffmpeg -i time.ts -c:v libx264 -c:a copy -to $CUT_POINT -map 0 -y before.ts

  Seems to be what I need. I think the re-encode is needed so the video can start at any arbitrary point and not an existing keyframe. If there’s a more efficient solution, that’s great. If not, this is good enough.

  EDIT : Here’s my attempt. I’m cobbling together various pieces I don’t fully understand copied from here. I’m leaving off the "cutting" piece for now to try and get audio + video encoded written without layering complexity. I get EXC_BAD_ACCESS on avcodec_encode_video2(...)

  - (void)convertInputPath:(NSString *)inputPath outputPath:(NSString *)outputPath
  
                   options:(NSDictionary *)options progressBlock:(FFmpegWrapperProgressBlock)progressBlock
  
           completionBlock:(FFmpegWrapperCompletionBlock)completionBlock {
  
      dispatch_async(conversionQueue, ^{
  
          FFInputFile *inputFile = nil;
  
          FFOutputFile *outputFile = nil;
  
          NSError *error = nil;
  
  
  
          inputFile = [[FFInputFile alloc] initWithPath:inputPath options:options];
  
          outputFile = [[FFOutputFile alloc] initWithPath:outputPath options:options];
  
  
  
          [self setupDirectStreamCopyFromInputFile:inputFile outputFile:outputFile];
  
          if (![outputFile openFileForWritingWithError:&error]) {
  
              [self finishWithSuccess:NO error:error completionBlock:completionBlock];
  
              return;
  
          }
  
          if (![outputFile writeHeaderWithError:&error]) {
  
              [self finishWithSuccess:NO error:error completionBlock:completionBlock];
  
              return;
  
          }
  
  
  
          AVRational default_timebase;
  
          default_timebase.num = 1;
  
          default_timebase.den = AV_TIME_BASE;
  
          FFStream *outputVideoStream = outputFile.streams[0];
  
          FFStream *inputVideoStream = inputFile.streams[0];
  
  
  
          AVFrame *frame;
  
          AVPacket inPacket, outPacket;
  
  
  
          frame = avcodec_alloc_frame();
  
          av_init_packet(&inPacket);
  
  
  
          while (av_read_frame(inputFile.formatContext, &inPacket) >= 0) {
  
              if (inPacket.stream_index == 0) {
  
                  int frameFinished;
  
                  avcodec_decode_video2(inputVideoStream.stream->codec, frame, &frameFinished, &inPacket);
  
  //                if (frameFinished && frame->pkt_pts >= starttime_int64 && frame->pkt_pts <= endtime_int64) {
  
                  if (frameFinished){
  
                      av_init_packet(&outPacket);
  
                      int output;
  
                      avcodec_encode_video2(outputVideoStream.stream->codec, &outPacket, frame, &output);
  
                      if (output) {
  
                          if (av_write_frame(outputFile.formatContext, &outPacket) != 0) {
  
                              fprintf(stderr, "convert(): error while writing video frame\n");
  
                              [self finishWithSuccess:NO error:nil completionBlock:completionBlock];
  
                          }
  
                      }
  
                      av_free_packet(&outPacket);
  
                  }
  
                  if (frame->pkt_pts > endtime_int64) {
  
                      break;
  
                  }
  
              }
  
          }
  
          av_free_packet(&inPacket);
  
  
  
          if (![outputFile writeTrailerWithError:&error]) {
  
              [self finishWithSuccess:NO error:error completionBlock:completionBlock];
  
              return;
  
          }
  
  
  
          [self finishWithSuccess:YES error:nil completionBlock:completionBlock];
  
      });
  
  }

• ffmpeg Command Fails in C

  16 février 2016, par cclloyd

  I have a program that stitches together files in ffmpeg using the system() function. It works when I run the command normally, but fails when I run it through the C program (it gets like 80% of the way through then fails saying

  [concat @ 0x7fe299801000] Impossible to open '/Us' parts.txt: No such file or directory
  
  No more output streams to write to, finishing.

  But that only happens in the C program. Not when I run the exact same command manually.

  The command it’s running is

  char command[1024];
  
  sprintf(command, "ffmpeg -f concat -i parts.txt -c copy s%de%02d.ts", season, episode);
  
  system(command);

  And the parts.txt file is as follows : http://pastebin.com/pUAu9mbt

  (Before you ask, yes those are absolute pathnames, not relative)

• AVSampleBufferDisplayLayer with VTDecompressionSession

  7 juillet 2016, par user1784317

  I’ve been struggling with AVSampleBufferDisplayLayer being really choppy with a lot of motion. When there was motion in my live stream, it would be come pixelated and half frozen with multiple frames displaying at once. However, once I added the following piece of code, everything was solved :

  VTDecodeFrameFlags flags = kVTDecodeFrame_EnableAsynchronousDecompression 
  
  | kVTDecodeFrame_EnableTemporalProcessing;
  
  VTDecodeInfoFlags flagOut;
  
  VTDecompressionSessionDecodeFrame(decompressionSession, sampleBuffer, flags,
  
  (void*)CFBridgingRetain(NULL), &flagOut);

  Note that I did create the decompression session before, but I don’t actually do anything in the callback. I am still calling enqueueSampleBuffer : on AVSampleBufferDisplayLayer and that is how the video is displayed on the screen.

  Do you have to call VTDecompressionSessionDecodeFrame for AVSampleBufferDisplayLayer to display correctly ? I thought AVSampleBufferDisplayLayerr would use VTDecompressionSessionDecodeFrame internally. Is this due to being on the iOS Simulator ?