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• doc : clarify option on looping infinitely in movie filter

  2 février 2017, par Werner Robitza

  doc : clarify option on looping infinitely in movie filter
  Clarify that setting loop=0 is required to make the stream loop infinitely, rather than saying that a value "less than 1" is needed.
  Signed-off-by : Lou Logan <lou@lrcd.com>
  

  • [DH] doc/filters.texi

• "invalid argument" for av_buffersrc_write_frame / av_buffersrc_add_frame

  1er février 2017, par TheSHEEEP

  I am trying to use FFmpeg C api to create a filter to merge two audio streams. Trying to follow the code from here : Implementing a multiple input filter graph with the Libavfilter library in Android NDK

  Everything seems to be alright.

  However, as soon as I call av_buffersrc_write_frame (or av_buffersrc_add_frame or av_buffersrc_add_frame_flags, it doesn’t matter), FFmpeg just reports "invalid argument" and nothing else - an utterly useless error message, as it could mean everything.
  Which argument is invalid ? What is wrong about it ? Nobody knows.

  I am initializing the graph and "grabbing" the contexts of the buffer sources for later use like this :

  // Alloc filter graph
  
  *filter_graph = avfilter_graph_alloc();
  
  if ((*filter_graph) == NULL) {
  
      os::log("Error: Cannot allocate filter graph.");
  
      return AVERROR(ENOMEM);
  
  }
  
  
  
  // Building the filter string, ommitted
  
  
  
  int result = avfilter_graph_parse2(*filter_graph, filterString.c_str(), &gis, &gos, NULL);
  
  if (result < 0)
  
  {
  
      char errorBuf[1024];
  
      av_make_error_string(errorBuf, 1024, result);
  
      log("Error: Parsing filter string: %s", errorBuf);
  
      return AVERROR_EXIT;
  
  }
  
  
  
  // Configure the graph
  
  result = avfilter_graph_config(*filter_graph, NULL);
  
  if (result < 0)
  
  {
  
      char errorBuf[1024];
  
      av_make_error_string(errorBuf, 1024, result);
  
      log("Error: Configuring filter graph: %s", errorBuf);
  
      return AVERROR_EXIT;
  
  }
  
  
  
  // Get the buffer source and buffer sink contexts
  
  for (unsigned int i = 0; i < (*filter_graph)->nb_filters; ++i) {
  
      AVFilterContext* filterContext = (*filter_graph)->filters[i];
  
  
  
      // The first two filters should be the abuffers
  
      std::string name = filterContext->name;
  
      if (name.find("abuffer") != name.npos && i < 2) {
  
          inputs[i].buffer_source_context = filterContext;
  
      }
  
  
  
      // abuffersink is the one we need to get the converted frames from
  
      if (name.find("abuffersink") != name.npos) {
  
          *buffer_sink_context = filterContext;
  
      }
  
  }

  There are absolutely no errors in the initialization. At least FFmpeg has only this to say about it, which I think looks good :

  FFMPEG: [Parsed_abuffer_0 @ 0ddfe840] Setting 'time_base' to value '1/48000'
  
  FFMPEG: [Parsed_abuffer_0 @ 0ddfe840] Setting 'sample_rate' to value '48000'
  
  FFMPEG: [Parsed_abuffer_0 @ 0ddfe840] Setting 'sample_fmt' to value '1'
  
  FFMPEG: [Parsed_abuffer_0 @ 0ddfe840] Setting 'channel_layout' to value '3'
  
  FFMPEG: [Parsed_abuffer_0 @ 0ddfe840] Setting 'channels' to value '2'
  
  FFMPEG: [Parsed_abuffer_0 @ 0ddfe840] tb:1/48000 samplefmt:s16 samplerate:48000 chlayout:3
  
  FFMPEG: [Parsed_abuffer_1 @ 0ddfe500] Setting 'time_base' to value '1/44100'
  
  FFMPEG: [Parsed_abuffer_1 @ 0ddfe500] Setting 'sample_rate' to value '44100'
  
  FFMPEG: [Parsed_abuffer_1 @ 0ddfe500] Setting 'sample_fmt' to value '1'
  
  FFMPEG: [Parsed_abuffer_1 @ 0ddfe500] Setting 'channel_layout' to value '3'
  
  FFMPEG: [Parsed_abuffer_1 @ 0ddfe500] Setting 'channels' to value '2'
  
  FFMPEG: [Parsed_abuffer_1 @ 0ddfe500] tb:1/44100 samplefmt:s16 samplerate:44100 chlayout:3
  
  FFMPEG: [Parsed_volume_3 @ 0ddfe580] Setting 'volume' to value '2'
  
  FFMPEG: [Parsed_aresample_4 @ 0ddfe660] Setting 'sample_rate' to value '48000'
  
  FFMPEG: [Parsed_aformat_5 @ 0ddfe940] Setting 'sample_fmts' to value 'fltp'
  
  FFMPEG: [Parsed_aformat_5 @ 0ddfe940] Setting 'channel_layouts' to value '3'

  Then, I am trying to add a frame (that has been decoded beforehand) like this :

  // "buffer_source_context" is one of the "inputs[i].buffer_source_context" from the code above
  
  int result = av_buffersrc_write_frame(  buffer_source_context,
  
                                              input_frame);
  
  if (result < 0) {
  
      char errorBuf[1024];
  
      av_make_error_string(errorBuf, 1024, result);
  
      log("Error: While adding to buffer source: %s", errorBuf);
  
      return AVERROR_EXIT;
  
  }

  And the result is the mentioned "invalid argument".

  The buffer_source_context is one of those noted from the code above and the input_frame is perfectly fine as well.
  Before the filtering code was added, the same frame was passed to an encoder instead without a problem.

  I am at a loss at what the error could be here. I log FFmpeg errors at the lowest possible level, but not a single error is shown. I am using FFmpeg 3.1.1.

• How to cheaply "undo" a mosaic (i.e. split an image into halves or quadrants) with ffmpeg ?

  5 mars 2020, par John Allard

  FFMPEG makes it easy to take multiple inputs and stack them into a mosaic video. I am looking for a way to do the opposite, specifically I would like take a video stream that is composed of four streams stacked into quadrants and split it into four separate videos consisting of the coordinates

  video1 = [0, 0.5*w, 0, 0.5*h]
  
  video2 = [0.5*w, w, 0, 0.5*h]
  
  video3 = [0, 0.5*w, 0.5*h, h]
  
  video4 = [0.5*w, w, 0.5*h, h]

  I know that I can do this with four separate ffmpeg calls using the crop filter but this seems to be unnecessarily expensive. Is there a way to do this in a single call ?