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• libavcodec/libx264 do not produce B-frames

  6 novembre 2013, par Rob Schmidt

  I am writing an application in C++ that uses libavcodec with libx264 to encode video. However, the encoded data ended up being much larger than I expected. I analyzed the results and discovered that my encoding never produced B-frames, only I- and P-frames.

  I created a standalone utility based on the ffmpeg source code and examples to test my encoder setup. It reads in an H.264 file, re-encodes the decoded frames, and outputs the result to a file using the ITU H.264 Annex B format. I also used ffmpeg to perform the same operation so I could compare against a known good implementation. My utility never outputs B-frames whereas ffmpeg does.

  I have since tried to figure out what ffmpeg does that my code doesn't. I first tried manually specifying encoder settings related to B-frames. This had no effect.

  I then tried running both ffmpeg and my utility under gdb and comparing the contents of the AVStream, AVCodecContext, and X264Context prior to opening the encoder and manually setting any fields that appeared different. Even with identical settings, I still only produce I- and P-frames.

  Finally, I thought that perhaps the problem was with my timestamp handling. I reworked my test utility to mimic the pipeline used by ffmpeg and to output timestamp debugging output like ffmpeg does. Even with my timestamps identical to ffmpeg's I still get no B-frames.

  At this point I don't know what else to try. When I run ffmpeg, I run it with the command line below. Note that aside from the "superfast" preset, I pretty much use the default values.

  ffmpeg -v debug -i ~/annexb.264 -codec:v libx264 -preset superfast -g 30 -f h264 ./out.264

  The code that configures the encoder is listed below. It specifies the "superfast" preset too.

  static AVStream *add_video_stream(AVFormatContext *output_ctx, AVCodec **output_codec, enum AVCodecID codec_id)
  
  {
  
      *output_codec = avcodec_find_encoder(codec_id);
  
      if (*output_codec == NULL) {
  
          printf("Could not find encoder for '%s' (%d)\n", avcodec_get_name(codec_id), codec_id);
  
          return NULL;
  
      }
  
  
  
      AVStream *output_stream = avformat_new_stream(output_ctx, *output_codec);
  
      if (output_stream == NULL) {
  
          printf("Could not create video stream.\n");
  
          return NULL;
  
      }
  
      output_stream->id = output_ctx->nb_streams - 1;
  
      AVCodecContext *codec_ctx = output_stream->codec;
  
  
  
      avcodec_get_context_defaults3(codec_ctx, *output_codec);
  
  
  
      codec_ctx->width = 1280;
  
      codec_ctx->height = 720;
  
  
  
      codec_ctx->time_base.den = 15000;
  
      codec_ctx->time_base.num = 1001;
  
  
  
  /*    codec_ctx->gop_size = 30;*/
  
      codec_ctx->pix_fmt = AV_PIX_FMT_YUVJ420P;
  
  
  
      // try to force B-frame output
  
  /*    codec_ctx->max_b_frames = 3;*/
  
  /*    codec_ctx->b_frame_strategy = 2;*/
  
  
  
      output_stream->sample_aspect_ratio.num = 1;
  
      output_stream->sample_aspect_ratio.den = 1;
  
  
  
      codec_ctx->sample_aspect_ratio.num = 1;
  
      codec_ctx->sample_aspect_ratio.den = 1;
  
  
  
      codec_ctx->chroma_sample_location = AVCHROMA_LOC_LEFT;
  
  
  
      codec_ctx->bits_per_raw_sample = 8;
  
  
  
      if ((output_ctx->oformat->flags & AVFMT_GLOBALHEADER) != 0) {
  
          codec_ctx->flags |= CODEC_FLAG_GLOBAL_HEADER;
  
      }
  
  
  
      return output_stream;
  
  }
  
  
  
  
  
  int main(int argc, char **argv)
  
  {
  
      // ... open input file 
  
  
  
      avformat_alloc_output_context2(&output_ctx, NULL, "h264", output_path);
  
      if (output_ctx == NULL) {
  
          fprintf(stderr, "Unable to allocate output context.\n");
  
          return 1;
  
      } 
  
  
  
      AVCodec *output_codec = NULL;
  
      output_stream = add_video_stream(output_ctx, &output_codec, output_ctx->oformat->video_codec);
  
      if (output_stream == NULL) {
  
          fprintf(stderr, "Error adding video stream to output context.\n");
  
          return 1;
  
      }
  
      encode_ctx = output_stream->codec;
  
  
  
      // seems to have no effect
  
  #if 0
  
      if (decode_ctx->extradata_size != 0) {
  
          size_t extradata_size = decode_ctx->extradata_size;
  
          printf("extradata_size: %zu\n", extradata_size);
  
          encode_ctx->extradata = av_mallocz(extradata_size + FF_INPUT_BUFFER_PADDING_SIZE);
  
          memcpy(encode_ctx->extradata, decode_ctx->extradata, extradata_size);
  
          encode_ctx->extradata_size = extradata_size;
  
      }
  
  #endif // 0
  
  
  
      AVDictionary *opts = NULL;
  
      av_dict_set(&opts, "preset", "superfast", 0);
  
      // av_dict_set(&opts, "threads", "auto", 0); // seems to have no effect
  
  
  
      ret = avcodec_open2(encode_ctx, output_codec, &opts);
  
      if (ret < 0) {
  
          fprintf(stderr, "Unable to open output video cocec: %s\n", av_err2str(ret));
  
          return 1;
  
      }
  
  
  
      // ... decoding/encoding loop, clean up, etc.
  
  
  
      return 0;
  
  }

  My test utility produces the following debug output in which you can see there are no B-frames produced :

  [libx264 @ 0x1b8c9c0] using mv_range_thread = 56
  
  [libx264 @ 0x1b8c9c0] using SAR=1/1
  
  [libx264 @ 0x1b8c9c0] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX
  
  [libx264 @ 0x1b8c9c0] profile High, level 3.1
  
  Output #0, h264, to './out.264':
  
      Stream #0:0, 0, 1/90000: Video: h264, yuvj420p, 1280x720 [SAR 1:1 DAR 16:9], 1001/15000, q=-1--1, 90k tbn, 14.99 tbc
  
  
  
  <snip>
  
  
  
  [libx264 @ 0x1b8c9c0] frame=   0 QP=17.22 NAL=3 Slice:I Poc:0   I:3600 P:0    SKIP:0    size=122837 bytes
  
  [libx264 @ 0x1b8c9c0] frame=   1 QP=18.03 NAL=2 Slice:P Poc:2   I:411  P:1825 SKIP:1364 size=25863 bytes
  
  [libx264 @ 0x1b8c9c0] frame=   2 QP=17.03 NAL=2 Slice:P Poc:4   I:369  P:2159 SKIP:1072 size=37880 bytes
  
  [libx264 @ 0x1b8c9c0] frame=   3 QP=16.90 NAL=2 Slice:P Poc:6   I:498  P:2330 SKIP:772  size=50509 bytes
  
  [libx264 @ 0x1b8c9c0] frame=   4 QP=16.68 NAL=2 Slice:P Poc:8   I:504  P:2233 SKIP:863  size=50791 bytes
  
  [libx264 @ 0x1b8c9c0] frame=   5 QP=16.52 NAL=2 Slice:P Poc:10  I:513  P:2286 SKIP:801  size=51820 bytes
  
  [libx264 @ 0x1b8c9c0] frame=   6 QP=16.49 NAL=2 Slice:P Poc:12  I:461  P:2293 SKIP:846  size=51311 bytes
  
  [libx264 @ 0x1b8c9c0] frame=   7 QP=16.65 NAL=2 Slice:P Poc:14  I:476  P:2287 SKIP:837  size=51196 bytes
  
  [libx264 @ 0x1b8c9c0] frame=   8 QP=16.66 NAL=2 Slice:P Poc:16  I:508  P:2240 SKIP:852  size=51577 bytes
  
  [libx264 @ 0x1b8c9c0] frame=   9 QP=16.55 NAL=2 Slice:P Poc:18  I:477  P:2278 SKIP:845  size=51531 bytes
  
  [libx264 @ 0x1b8c9c0] frame=  10 QP=16.67 NAL=2 Slice:P Poc:20  I:517  P:2233 SKIP:850  size=51946 bytes
  
  
  
  <snip>
  
  
  
  [libx264 @ 0x1b8c9c0] frame I:7     Avg QP:13.71  size:152207
  
  [libx264 @ 0x1b8c9c0] frame P:190   Avg QP:16.66  size: 50949
  
  [libx264 @ 0x1b8c9c0] mb I  I16..4: 27.1% 30.8% 42.1%
  
  [libx264 @ 0x1b8c9c0] mb P  I16..4:  6.8%  6.0%  0.8%  P16..4: 61.8%  0.0%  0.0%  0.0%  0.0%    skip:24.7%
  
  [libx264 @ 0x1b8c9c0] 8x8 transform intra:41.2% inter:86.9%
  
  [libx264 @ 0x1b8c9c0] coded y,uvDC,uvAC intra: 92.2% 28.3% 5.4% inter: 50.3% 1.9% 0.0%
  
  [libx264 @ 0x1b8c9c0] i16 v,h,dc,p:  7%  7% 77%  8%
  
  [libx264 @ 0x1b8c9c0] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu:  7% 15% 49%  6%  4%  3%  5%  3%  8%
  
  [libx264 @ 0x1b8c9c0] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 19% 25% 24%  6%  7%  4%  6%  3%  6%
  
  [libx264 @ 0x1b8c9c0] i8c dc,h,v,p: 72% 14% 10%  4%
  
  [libx264 @ 0x1b8c9c0] Weighted P-Frames: Y:0.0% UV:0.0%
  
  [libx264 @ 0x1b8c9c0] kb/s:6539.11
  
  </snip></snip>

  ffmpeg, on the other hand, produces the following output that is almost identical but includes B-frames :

  [libx264 @ 0x20b9c40] using mv_range_thread = 56
  
  [libx264 @ 0x20b9c40] using SAR=1/1
  
  [libx264 @ 0x20b9c40] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX
  
  [libx264 @ 0x20b9c40] profile High, level 3.1
  
  [h264 @ 0x20b8160] detected 4 logical cores
  
  Output #0, h264, to './out.264':
  
    Metadata:
  
      encoder         : Lavf54.63.104
  
      Stream #0:0, 0, 1/90000: Video: h264, yuvj420p, 1280x720 [SAR 1:1 DAR 16:9], 1001/15000, q=-1--1, 90k tbn, 14.99 tbc
  
  Stream mapping:
  
    Stream #0:0 -> #0:0 (h264 -> libx264)
  
  
  
  <snip>
  
  
  
  [libx264 @ 0x20b9c40] frame=   0 QP=17.22 NAL=3 Slice:I Poc:0   I:3600 P:0    SKIP:0    size=122835 bytes
  
  [libx264 @ 0x20b9c40] frame=   1 QP=18.75 NAL=2 Slice:P Poc:8   I:984  P:2045 SKIP:571  size=54208 bytes
  
  [libx264 @ 0x20b9c40] frame=   2 QP=19.40 NAL=2 Slice:B Poc:4   I:447  P:1581 SKIP:1572 size=24930 bytes
  
  [libx264 @ 0x20b9c40] frame=   3 QP=19.78 NAL=0 Slice:B Poc:2   I:199  P:1002 SKIP:2399 size=10717 bytes
  
  [libx264 @ 0x20b9c40] frame=   4 QP=20.19 NAL=0 Slice:B Poc:6   I:204  P:1155 SKIP:2241 size=15937 bytes
  
  [libx264 @ 0x20b9c40] frame=   5 QP=18.11 NAL=2 Slice:P Poc:16  I:990  P:2221 SKIP:389  size=64240 bytes
  
  [libx264 @ 0x20b9c40] frame=   6 QP=19.35 NAL=2 Slice:B Poc:12  I:439  P:1784 SKIP:1377 size=34048 bytes
  
  [libx264 @ 0x20b9c40] frame=   7 QP=19.88 NAL=0 Slice:B Poc:10  I:275  P:1035 SKIP:2290 size=16911 bytes
  
  [libx264 @ 0x20b9c40] frame=   8 QP=19.91 NAL=0 Slice:B Poc:14  I:257  P:1270 SKIP:2073 size=19172 bytes
  
  [libx264 @ 0x20b9c40] frame=   9 QP=17.90 NAL=2 Slice:P Poc:24  I:962  P:2204 SKIP:434  size=67439 bytes
  
  [libx264 @ 0x20b9c40] frame=  10 QP=18.84 NAL=2 Slice:B Poc:20  I:474  P:1911 SKIP:1215 size=37742 bytes
  
  
  
  <snip>
  
  
  
  [libx264 @ 0x20b9c40] frame I:7     Avg QP:15.95  size:130124
  
  [libx264 @ 0x20b9c40] frame P:52    Avg QP:17.78  size: 64787
  
  [libx264 @ 0x20b9c40] frame B:138   Avg QP:19.32  size: 26231
  
  [libx264 @ 0x20b9c40] consecutive B-frames:  6.6%  0.0%  0.0% 93.4%
  
  [libx264 @ 0x20b9c40] mb I  I16..4: 30.2% 35.2% 34.6%
  
  [libx264 @ 0x20b9c40] mb P  I16..4: 13.9% 11.4%  0.3%  P16..4: 60.4%  0.0%  0.0%  0.0%  0.0%    skip:13.9%
  
  [libx264 @ 0x20b9c40] mb B  I16..4:  5.7%  3.3%  0.0%  B16..8: 15.8%  0.0%  0.0%  direct:25.7%  skip:49.5%  L0:43.2% L1:37.3% BI:19.5%
  
  [libx264 @ 0x20b9c40] 8x8 transform intra:39.4% inter:77.2%
  
  [libx264 @ 0x20b9c40] coded y,uvDC,uvAC intra: 90.7% 26.6% 3.0% inter: 34.0% 4.1% 0.0%
  
  [libx264 @ 0x20b9c40] i16 v,h,dc,p:  7%  7% 77%  9%
  
  [libx264 @ 0x20b9c40] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu:  7% 16% 51%  5%  4%  3%  5%  3%  7%
  
  [libx264 @ 0x20b9c40] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 22% 27% 20%  6%  6%  3%  6%  3%  6%
  
  [libx264 @ 0x20b9c40] i8c dc,h,v,p: 71% 15% 11%  3%
  
  [libx264 @ 0x20b9c40] Weighted P-Frames: Y:0.0% UV:0.0%
  
  [libx264 @ 0x20b9c40] kb/s:4807.16
  
  </snip></snip>

  I'm sure I'm missing something simple, but I can't for the life of me see what it is. Any assistance would be greatly appreciated.

• iPhone camera shooting video using the AVCaptureSession and using ffmpeg CMSampleBufferRef a change in h.264 format is the issue. please advice

  4 janvier 2012, par isaiah

  My goal is h.264/AAC , mpeg2-ts streaming to server from iphone device.

  Current my source is FFmpeg+libx264 compile success. I Know gnu License. I want the demo program.

  I'm want to know that

  1.CMSampleBufferRef to AVPicture data is success ?

   avpicture_fill((AVPicture*)pFrame, rawPixelBase, PIX_FMT_RGB32, width, height);
  
    pFrame linesize and data is not null but pst -9233123123 . outpic also .
  
   Because of this I have to guess 'non-strictly-monotonic PTS' message 

  2.This log is repeat.

  encoding frame (size= 0)
  
  encoding frame = "" , 'avcodec_encode_video' return 0 is success but always 0 . 

  I don't know what to do...

  2011-06-01 15:15:14.199 AVCam[1993:7303] pFrame = avcodec_alloc_frame(); 
  
  2011-06-01 15:15:14.207 AVCam[1993:7303] avpicture_fill = 1228800
  
  Video encoding
  
  2011-0601 15:5:14.215 AVCam[1993:7303] codec = 5841844
  
  [libx264 @ 0x1441e00] using cpu capabilities: ARMv6 NEON
  
  [libx264 @ 0x1441e00] profile Constrained Baseline, level 2.0[libx264 @ 0x1441e00] non-strictly-monotonic PTS
  
  encoding frame (size=    0)
  
  encoding frame 
  
  [libx264 @ 0x1441e00] final ratefactor: 26.74

  3.I have to guess 'non-strictly-monotonic PTS' message is the cause of all problems.
  what is this 'non-strictly-monotonic PTS' .

   this is source 

  (void)        captureOutput:(AVCaptureOutput *)captureOutput 
  
          didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer 
  
                 fromConnection:(AVCaptureConnection *)connection
  
  {
  
  
  
      if( !CMSampleBufferDataIsReady(sampleBuffer) )
  
      {
  
          NSLog( @"sample buffer is not ready. Skipping sample" );
  
          return;
  
      }
  
  
  
  
  
      if( [isRecordingNow isEqualToString:@"YES"] )
  
      {
  
          lastSampleTime = CMSampleBufferGetPresentationTimeStamp(sampleBuffer);
  
          if( videoWriter.status != AVAssetWriterStatusWriting  )
  
          {
  
              [videoWriter startWriting];
  
              [videoWriter startSessionAtSourceTime:lastSampleTime];
  
          }
  
  
  
          if( captureOutput == videooutput )
  
          {
  
              [self newVideoSample:sampleBuffer];
  
  
  
              CVImageBufferRef pixelBuffer = CMSampleBufferGetImageBuffer(sampleBuffer); 
  
              CVPixelBufferLockBaseAddress(pixelBuffer, 0); 
  
  
  
              // access the data 
  
              int width = CVPixelBufferGetWidth(pixelBuffer); 
  
              int height = CVPixelBufferGetHeight(pixelBuffer); 
  
              unsigned char *rawPixelBase = (unsigned char *)CVPixelBufferGetBaseAddress(pixelBuffer); 
  
  
  
              AVFrame *pFrame; 
  
              pFrame = avcodec_alloc_frame(); 
  
              pFrame->quality = 0;
  
  
  
              NSLog(@"pFrame = avcodec_alloc_frame(); ");
  
  
  
  //          int bytesPerRow = CVPixelBufferGetBytesPerRowOfPlane(pixelBuffer, 0);
  
  
  
  //          int bytesSize = height * bytesPerRow ;  
  
  
  
  //          unsigned char *pixel = (unsigned char*)malloc(bytesSize);
  
  
  
  //          unsigned char *rowBase = CVPixelBufferGetBaseAddressOfPlane(pixelBuffer, 0);
  
  
  
  //          memcpy (pixel, rowBase, bytesSize);
  
  
  
  
  
              int avpicture_fillNum = avpicture_fill((AVPicture*)pFrame, rawPixelBase, PIX_FMT_RGB32, width, height);//PIX_FMT_RGB32//PIX_FMT_RGB8
  
              //NSLog(@"rawPixelBase = %i , rawPixelBase -s = %s",rawPixelBase, rawPixelBase); 
  
              NSLog(@"avpicture_fill = %i",avpicture_fillNum);
  
              //NSLog(@"width = %i,height = %i",width, height);
  
  
  
  
  
  
  
              // Do something with the raw pixels here 
  
  
  
              CVPixelBufferUnlockBaseAddress(pixelBuffer, 0); 
  
  
  
              //avcodec_init();
  
              //avdevice_register_all();
  
              av_register_all();
  
  
  
  
  
  
  
  
  
  
  
              AVCodec *codec;
  
              AVCodecContext *c= NULL;
  
              int  out_size, size, outbuf_size;
  
              //FILE *f;
  
              uint8_t *outbuf;
  
  
  
              printf("Video encoding\n");
  
  
  
              /* find the mpeg video encoder */
  
              codec =avcodec_find_encoder(CODEC_ID_H264);//avcodec_find_encoder_by_name("libx264"); //avcodec_find_encoder(CODEC_ID_H264);//CODEC_ID_H264);
  
              NSLog(@"codec = %i",codec);
  
              if (!codec) {
  
                  fprintf(stderr, "codec not found\n");
  
                  exit(1);
  
              }
  
  
  
              c= avcodec_alloc_context();
  
  
  
              /* put sample parameters */
  
              c->bit_rate = 400000;
  
              c->bit_rate_tolerance = 10;
  
              c->me_method = 2;
  
              /* resolution must be a multiple of two */
  
              c->width = 352;//width;//352;
  
              c->height = 288;//height;//288;
  
              /* frames per second */
  
              c->time_base= (AVRational){1,25};
  
              c->gop_size = 10;//25; /* emit one intra frame every ten frames */
  
              //c->max_b_frames=1;
  
              c->pix_fmt = PIX_FMT_YUV420P;
  
  
  
              c ->me_range = 16;
  
              c ->max_qdiff = 4;
  
              c ->qmin = 10;
  
              c ->qmax = 51;
  
              c ->qcompress = 0.6f;
  
  
  
              /* open it */
  
              if (avcodec_open(c, codec) < 0) {
  
                  fprintf(stderr, "could not open codec\n");
  
                  exit(1);
  
              }
  
  
  
  
  
              /* alloc image and output buffer */
  
              outbuf_size = 100000;
  
              outbuf = malloc(outbuf_size);
  
              size = c->width * c->height;
  
  
  
              AVFrame* outpic = avcodec_alloc_frame();
  
              int nbytes = avpicture_get_size(PIX_FMT_YUV420P, c->width, c->height);
  
  
  
              //create buffer for the output image
  
              uint8_t* outbuffer = (uint8_t*)av_malloc(nbytes);
  
  
  
  #pragma mark -  
  
  
  
              fflush(stdout);
  
  
  
  <pre>//         int numBytes = avpicture_get_size(PIX_FMT_YUV420P, c->width, c->height);
  
  //          uint8_t *buffer = (uint8_t *)av_malloc(numBytes*sizeof(uint8_t));
  
  //          
  
  //          //UIImage *image = [UIImage imageNamed:[NSString stringWithFormat:@"10%d", i]];
  
  //          CGImageRef newCgImage = [self imageFromSampleBuffer:sampleBuffer];//[image CGImage];
  
  //          
  
  //          CGDataProviderRef dataProvider = CGImageGetDataProvider(newCgImage);
  
  //          CFDataRef bitmapData = CGDataProviderCopyData(dataProvider);
  
  //          buffer = (uint8_t *)CFDataGetBytePtr(bitmapData);   
  
  //          
  
  //          avpicture_fill((AVPicture*)pFrame, buffer, PIX_FMT_RGB8, c->width, c->height);
  
              avpicture_fill((AVPicture*)outpic, outbuffer, PIX_FMT_YUV420P, c->width, c->height);
  
  
  
              struct SwsContext* fooContext = sws_getContext(c->width, c->height, 
  
                                                             PIX_FMT_RGB8, 
  
                                                             c->width, c->height, 
  
                                                             PIX_FMT_YUV420P, 
  
                                                             SWS_FAST_BILINEAR, NULL, NULL, NULL);
  
  
  
              //perform the conversion
  
              sws_scale(fooContext, pFrame->data, pFrame->linesize, 0, c->height, outpic->data, outpic->linesize);
  
              // Here is where I try to convert to YUV
  
  
  
              /* encode the image */
  
  
  
              out_size = avcodec_encode_video(c, outbuf, outbuf_size, outpic);
  
              printf("encoding frame (size=%5d)\n", out_size);
  
              printf("encoding frame %s\n", outbuf);
  
  
  
  
  
              //fwrite(outbuf, 1, out_size, f);
  
  
  
              //              free(buffer);
  
              //              buffer = NULL;      
  
  
  
  
  
  
  
              /* add sequence end code to have a real mpeg file */
  
  //          outbuf[0] = 0x00;
  
  //          outbuf[1] = 0x00;
  
  //          outbuf[2] = 0x01;
  
  //          outbuf[3] = 0xb7;
  
              //fwrite(outbuf, 1, 4, f);
  
              //fclose(f);
  
              free(outbuf);
  
  
  
              avcodec_close(c);
  
              av_free(c);
  
              av_free(pFrame);
  
              printf("\n");
  
  </pre>

• Error while opening encoder for output stream #0:1 - maybe incorrect parameters such as bit_rate, rate, width or height

  7 janvier 2012, par Rocky Singh

  I am trying to convert an avi video file to flv format via FFMPEG with the following command :

  -i C:\files\input\test.avi -y -ab 448k -ar 48000 -vcodec mpeg4 -s 640x480 -f flv C:\files\output\test.flv

  Here is the response I am getting from ffmpeg :

  Input :

  Input #0, avi, from 'C:\files\input\test.avi':
  
    Metadata:
  
      encoder         : VirtualDubMod 1.5.10.2 (build 2540/release)
  
    Duration: 00:01:00.00, start: 0.000000, bitrate: 1813 kb/s
  
      Stream #0:0: Video: mpeg4 (Advanced Simple Profile) (XVID / 0x44495658), yuv420p, 640x272 [SAR 1:1 DAR 40:17], 25 tbr, 25 tbn, 25 tbc
  
      Stream #0:1: Audio: ac3 ([0] [0][0] / 0x2000), 48000 Hz, 5.1(side), s16, 448 kb/s

  Output :

  Output #0, flv, to 'C:\files\output\test.flv':
  
    Metadata:
  
      encoder         : VirtualDubMod 1.5.10.2 (build 2540/release)
  
      Stream #0:0: Video: mpeg4, yuv420p, 640x480 [SAR 30:17 DAR 40:17], q=2-31, 200 kb/s, 90k tbn, 25 tbc
  
      Stream #0:1: Audio: mp3, 48000 Hz, 5.1(side), s16, 448 kb/s
  
  Stream mapping:
  
    Stream #0:0 -> #0:0 (mpeg4 -> mpeg4)
  
    Stream #0:1 -> #0:1 (ac3 -> libmp3lame)
  
  Error while opening encoder for output stream #0:1 - maybe incorrect parameters such as bit_rate, rate, width or height

  Can you tell me what is MAY BE here ? and what is wrong above ?