Recherche avancée

Sur d’autres sites (3389)

• ffmpeg quality conversion options (video compression)

  25 septembre 2020, par Jason Hunter

  Can you provide a link, or an explanation, to the -q:v 1 argument that deals with video/image quality, and compression, in ffmpeg.

  


  Let me explain...

  


  for f in *
   do 
     extension="${f##*.}"
     filename="${f%.*}"
     ffmpeg -i "$f" -q:v 1 "$filename"_lq."$extension"
     rm -f "$f"
   done


  


  The ffmpeg for loop above compresses all images and videos in your working directory, it basically lowers the quality which results in smaller file sizes (the desired outcome).

  


  I'm most interested in the -q:v 1 argument of this for loop. The 1 in the -q:v 1 argument is what controls the amount of compression. But I can't find any documentation describing how to change this value of 1, and describing what it does. Is it a percentage ? Multiplier ? How do I adjust this knob ? Can/should I use negative values ? Integers only ? Min/max values ? etc.

  


  I started with the official documentation but the best I could find was a section on video quality, and the -q flag description is sparse.

  


  


  -frames[:stream_specifier] framecount (output,per-stream)
  
Stop writing to the stream after framecount frames.
  
.
  
-q[:stream_specifier] q (output,per-stream)
  

  
-qscale[:stream_specifier] q (output,per-stream)
  
Use fixed quality scale (VBR). The meaning of q/qscale is codec-dependent. If qscale is used without a stream_specifier then it applies only to the video stream, this is to maintain compatibility with previous behavior and as specifying the same codec specific value to 2 different codecs that is audio and video generally is not what is intended when no stream_specifier is used.

  


  


• aacenc_tns : remove unused header

  22 août 2015, par Rostislav Pehlivanov

  aacenc_tns : remove unused header
  Thanks to @nevcairiel for pointing this one out.
  
  Another thing which stopped msvc from compiling.
  Signed-off-by : Rostislav Pehlivanov <atomnuker@gmail.com>
  

  • [DH] libavcodec/aacenc_tns.c

• FFmpeg, access violation on av_frame_free when running though Unity

  27 octobre 2016, par Mockarutan

  I’m working on a video recording plugin for Unity using ffmpeg. I’m new to the video encoding domain and just got my code to work today. But I think a might have a few memory leaks and trying to fix them crashes Unity.

  The plugin is written i c++ (as external "C" code) and imported in a c# script in unity with a simple DllImport. Again, this is not my comfort area either, but it works.

  When a screen buffer is rendered, I put in a RGB24 buffer and send it to my c++ function, this one :

  int encode_frame(uint8_t* rgb24Data)
  
  {
  
      AVFrame *frame = av_frame_alloc();
  
      if (!frame)
  
          return COULD_NOT_ALLOCATE_FRAME;
  
  
  
      frame->format = codec_context->pix_fmt;
  
      frame->width = codec_context->width;
  
      frame->height = codec_context->height;
  
  
  
      int ret = av_image_alloc(frame->data, frame->linesize, codec_context->width, codec_context->height, codec_context->pix_fmt, 32);
  
      if (ret < 0)
  
          return COULD_NOT_ALLOCATE_PIC_BUF;
  
  
  
      SwsContext * ctx = sws_getContext(codec_context->width, codec_context->height,
  
          AV_PIX_FMT_RGB24, codec_context->width, codec_context->height,
  
          AV_PIX_FMT_YUV420P, 0, 0, 0, 0);
  
  
  
  
  
      uint8_t * inData[1] = { rgb24Data };
  
      int inLinesize[1] = { 3 * codec_context->width };
  
  
  
      sws_scale(ctx, inData, inLinesize, 0, codec_context->height, frame->data, frame->linesize); // From RGB to YUV
  
  
  
      frame->pts = frame_counter++;
  
  
  
      ret = avcodec_send_frame(codec_context, frame);
  
      if (ret < 0)
  
          return ERROR_ENCODING_FRAME_SEND;
  
  
  
      AVPacket pkt;
  
      av_init_packet(&pkt);
  
      pkt.data = NULL;
  
      pkt.size = 0;
  
  
  
      while (true)
  
      {
  
          ret = avcodec_receive_packet(codec_context, &pkt);
  
          if (!ret)
  
          {
  
              if (pkt.pts != AV_NOPTS_VALUE)
  
                  pkt.pts = av_rescale_q(pkt.pts, codec_context->time_base, video_st->time_base);
  
              if (pkt.dts != AV_NOPTS_VALUE)
  
                  pkt.dts = av_rescale_q(pkt.dts, codec_context->time_base, video_st->time_base);
  
  
  
              av_write_frame(outctx, &pkt);
  
              av_packet_unref(&pkt);
  
          }
  
          else if (ret == AVERROR(EAGAIN))
  
          {
  
              frame->pts = frame_counter++;
  
              ret = avcodec_send_frame(codec_context, frame);
  
              if (ret < 0)
  
                  return ERROR_ENCODING_FRAME_SEND;
  
          }
  
          else if (ret < 0)
  
              return ERROR_ENCODING_FRAME_RECEIVE;
  
          else
  
              break;
  
      }
  
  
  
      // This one
  
      av_frame_free(&frame);
  
  }

  Now, this code might have a lot of issues that I’m not aware of, and you are free to point them out if you like. But the line that gives me error is av_frame_free(&frame);.

  If I run this in a synthetic test app in c++ that I made, it works. I can even run it in a c# synthetic test app (exactly like the c++ one), and it works. But if I run it though Unity, it crashes on the first frame. The log says "Read from location fe7f8097 caused an access violation.".

  I have tried with av_freep() and av_free(). Not sure exactly what makes them different (different example codes use different ones), but none work.

  So, what I’m I missing ? The frame is leaking if I don’t free it right ? But why does it crash in Unity ?

  The whole thing works great in Unity if I don’t have the av_frame_free(&frame);. Resulting video looks great !

  PS. I’m aware (as far as I know) that the frame also leaks if something fails and returns an error code. But one thing at a time.