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• encoding by using ffmpeg library

  22 août 2013, par Mustafe

  I am currently developing an application by using ffmpeg library. I have a problem with encoding pcm/raw datas. In ffmpeg/encoding_decoding.c source code, at line 146 in this function :

  buffer_size = av_samples_get_buffer_size(NULL, c->channels, c->frame_size, c->sample_fmt, 0);

  buffer_size is being calculated. My function always returns -22 which states an error. After a little examanation I noticed that in line 1888 at avcodec.h it is stated as following which shows the reason. Since CODEC_CAP_VARIABLE_FRAME_SIZE is set my function returns -22 and my program terminates. In this case the encoding code example in ffmpeg's website also could not work. How can I solve this problem ?

  encoding: set by libavcodec in avcodec_open2(). Each submitted frame except the last must contain exactly frame_size samples per channel. May be 0 when the codec has CODEC_CAP_VARIABLE_FRAME_SIZE set, then the frame size is not restricted. decoding: may be set by some decoders to indicate constant frame size

• Correct syntax for ffmpeg filter combination ?

  16 mai 2018, par shoku

  I’m playing with ffmpeg to generate a pretty video out of an mp3 + jpg.

  I’ve managed to generate a video that takes a jpg as a background, and adds a waveform complex filter on top of it (and removes the black bg as an overlay).

  This works :
  ffmpeg -y -i 1.mp3 -loop 1 -i 1.jpg -filter_complex "[0:a]showwaves=s=1280x720:mode=cline,colorkey=0x000000:0.01:0.1,format=yuva420p[v] ;[1:v][v]overlay[outv]" -map "[outv]" -pix_fmt yuv420p -map 0:a -c:v libx264 -c:a copy -shortest output.mp4

  I’ve been trying to add text somewhere in the generated video too. I’m trying the drawtext filter. I can’t get this to work however, so it seems I don’t understand the syntax, or how to combine filters.

  This doesn’t work :
  ffmpeg -y -i 1.mp3 -loop 1 -i 1.jpg -filter_complex "[0:a]showwaves=s=1280x720:mode=line,colorkey=0x000000:0.01:0.1,format=yuva420p[v] ;[1:v][v]overlay[outv]" -filter_complex "[v]drawtext=text=’My custom text test’:fontcolor=White@0.5 : fontsize=30:font=Arvo:x=(w-text_w)/5:y=(h-text_h)/5[out]" -map "[outv]" -pix_fmt yuv420p -map 0:a -c:v libx264 -c:a copy -shortest output.mp4

  Would love some pointers !

• encapsulating H.264 streams variable framerate in MPEG2 transport stream

  2 mai 2012, par user1058600

  Imagine I have H.264 AnxB frames coming in from a real-time conversation. What is the best way to encapsulate in MPEG2 transport stream while maintaining the timing information for subsequent playback ?

  I am using libavcodec and libavformat libraries. When I obtain pointer to object (*pcc) of type AVCodecContext, I set the foll.

  pcc->codec_id = CODEC_ID_H264;
  
  pcc->bit_rate = br;
  
  pcc->width = 640;
  
  pcc->height = 480;
  
  pcc->time_base.num = 1;
  
  pcc->time_base.den = fps;

  When I receive NAL units, I create a AVPacket and call av_interleaved_write_frame().

  AVPacket pkt;
  
  av_init_packet( &pkt );
  
  pkt.flags |= AV_PKT_FLAG_KEY;   
  
  pkt.stream_index = pst->index;
  
  pkt.data = (uint8_t*)p_NALunit;
  
  pkt.size = len;
  
  
  
  pkt.dts = AV_NOPTS_VALUE;
  
  pkt.pts = AV_NOPTS_VALUE;
  
  
  
  av_interleaved_write_frame( fc, &pkt );

  I basically have two questions :

  1) For variable framerate, is there a way to not specify the foll.
  pcc->time_base.num = 1 ;
  pcc->time_base.den = fps ;
  and replace it with something to indicate variable framerate ?

  2) While submitting packets, what "timestamps" should I assign to
  pkt.dts and pkt.pts ?

  Right now, when I play the output using ffplay it is playing at constant framerate (fps) which I use in the above code.

  I also would love to know how to accommodate varying spatial resolution. In the stream that I receive, each keyframe is preceded by SPS and PPS. I know whenever the spatial resolution changes.
  IS there a way to not have to specify
  pcc->width = 640 ;
  pcc->height = 480 ;
  upfront ? In other words, indicate that the spatial resolution can change mid-stream.

  Thanks a lot,
  Eddie