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• FFmpeg api iOS "Resource temporarily unavailable"

  8 octobre 2017, par Julius Naeumann

  I’ve spent hours trying to fix this :

  I’m trying to use the ffmpeg api on iOS. My Xcode project is building and I can call ffmpeg api functions. I am trying to write code that decodes a video (Without outputting anything for now), and I keep getting error -35 : "Resource temporarily unavailable".

  The input file is from the camera roll (.mov) and I’m using Mpeg-4 for decoding. All I’m currently doing is getting data from the file, parsing it and sending the parsed packets to the decoder. When I try to get frames, all I get is an error. Does anyone know what I’m doing wrong ?

  +(void)test: (NSString*)filename outfile:(NSString*)outfilename {
  
  
  
  /* register all the codecs */
  
  avcodec_register_all();
  
  
  
  AVCodec *codec;
  
  AVCodecParserContext *parser;
  
  AVCodecContext *c= NULL;
  
  int frame_count;
  
  FILE* f;
  
  AVFrame* frame;
  
  AVPacket* avpkt;
  
  avpkt = av_packet_alloc();
  
  //av_init_packet(avpkt);
  
  char buf[1024];
  
  
  
  uint8_t inbuf[INBUF_SIZE + AV_INPUT_BUFFER_PADDING_SIZE];
  
  uint8_t *data;
  
  size_t   data_size;
  
  
  
  /* set end of buffer to 0 (this ensures that no overreading happens for damaged mpeg streams) */
  
  memset(inbuf + INBUF_SIZE, 0, AV_INPUT_BUFFER_PADDING_SIZE);
  
  
  
  printf("Decode video file %s to %s\n", [filename cStringUsingEncoding:NSUTF8StringEncoding], [outfilename cStringUsingEncoding:NSUTF8StringEncoding]);
  
  /* find the h264 video decoder */
  
  codec = avcodec_find_decoder(AV_CODEC_ID_MPEG4);
  
  if (!codec) {
  
      fprintf(stderr, "Codec not found\n");
  
      exit(1);
  
  }
  
  c = avcodec_alloc_context3(codec);
  
  if (!c) {
  
      fprintf(stderr, "Could not allocate video codec context\n");
  
      exit(1);
  
  }
  
  if (codec->capabilities & AV_CODEC_CAP_TRUNCATED)
  
      c->flags |= AV_CODEC_FLAG_TRUNCATED; // we do not send complete frames
  
  /* For some codecs, such as msmpeg4 and mpeg4, width and height
  
   MUST be initialized there because this information is not
  
   available in the bitstream. */
  
  /* open it */
  
  if (avcodec_open2(c, codec, NULL) < 0) {
  
      fprintf(stderr, "Could not open codec\n");
  
      exit(1);
  
  }
  
  f = fopen([filename cStringUsingEncoding:NSUTF8StringEncoding], "rb");
  
  if (!f) {
  
      fprintf(stderr, "Could not open %s\n", [filename cStringUsingEncoding:NSUTF8StringEncoding]);
  
      exit(1);
  
  }
  
  frame = av_frame_alloc();
  
  if (!frame) {
  
      fprintf(stderr, "Could not allocate video frame\n");
  
      exit(1);
  
  }
  
  frame_count = 0;
  
  
  
  parser = av_parser_init(codec->id);
  
  if (!parser) {
  
      fprintf(stderr, "parser not found\n");
  
      exit(1);
  
  }
  
  
  
  while (!feof(f)) {
  
      /* read raw data from the input file */
  
      data_size = fread(inbuf, 1, INBUF_SIZE, f);
  
      if (!data_size)
  
          break;
  
      /* use the parser to split the data into frames */
  
      data = inbuf;
  
      while (data_size > 0) {
  
          int ret = av_parser_parse2(parser, c, &avpkt->data, &avpkt->size, data, data_size, AV_NOPTS_VALUE, AV_NOPTS_VALUE, 0);
  
          if (ret < 0) {
  
              fprintf(stderr, "Error while parsing\n");
  
              exit(1);
  
          }
  
          data      += ret;
  
          data_size -= ret;
  
          if (avpkt->size){
  
              char buf[1024];
  
  
  
              ret = avcodec_send_packet(c, avpkt);
  
              if (ret < 0) {
  
  
  
                  fprintf(stderr, "Error sending a packet for decoding\n");
  
                  continue;
  
                  exit(1);
  
              }
  
  
  
              while (ret >= 0) {
  
                  ret = avcodec_receive_frame(c, frame);
  
                  if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF){
  
                      char e [1024];
  
                      av_strerror(ret, e, 1024);
  
                      fprintf(stderr, "Fail: %s !\n", e);
  
  // ~~~~~~~~ This is where my program exits ~~~~~~~~~~~~~~~~~~~~~~~~~~~
  
                      return;
  
                  }
  
                  else if (ret < 0) {
  
                      fprintf(stderr, "Error during decoding\n");
  
                      exit(1);
  
                  }
  
              }
  
  
  
  
  
          }
  
      }
  
  }
  
  /* some codecs, such as MPEG, transmit the I and P frame with a
  
   latency of one frame. You must do the following to have a
  
   chance to get the last frame of the video */
  
  
  
  fclose(f);
  
  avcodec_close(c);
  
  av_free(c);
  
  av_frame_free(&frame);
  
  printf("\n");

  }

• h264 inside AVI, MP4 and "Raw" h264 streams. Different format of NAL units (or ffmpeg bug)

  24 octobre 2019, par bukkojot

  TL ;DR : I want to read raw h264 streams from AVI/MP4 files, even broken/incomplete.

  Almost every document about h264 tells me that it consists of NAL packets. Okay. Almost everywhere told to me that the packet should start with a signature like 00 00 01 or 00 00 00 01. For example, https://stackoverflow.com/a/18638298/8167678, https://stackoverflow.com/a/17625537/8167678

  The format of H.264 is that it’s made up of NAL Units, each starting
  with a start prefix of three bytes with the values 0x00, 0x00, 0x01
  and each unit has a different type depending on the value of the 4th
  byte right after these 3 starting bytes. One NAL Unit IS NOT one frame
  in the video, each frame is made up of a number of NAL Units.

  Okay.

  I downloaded random_youtube_video.mp4 and strip out one frame from it :

  ffmpeg -ss 10 -i random_youtube_video.mp4 -frames 1 -c copy pic.avi

  And got :
  
  Red part - this is part of AVI container, other - actual data.
  As you can see, here I have 00 00 24 A9 instead of 00 00 00 01

  This AVI file plays perfectly

  I do same for mp4 container :
  

  As you can see, here exact same bytes.
  This MP4 file plays perfectly

  I try to strip out raw data :
  ffmpeg -i pic.avi -c copy pic.h264
  

  This file can’t play in VLC or even ffmpeg, which produced this file, can’t parse it :
  

  I downloaded mp4 stream analyzer and got :
  

  MP4Box tells me :

   Cannot find H264 start code
  
   Error importing pic.h264: BitStream Not Compliant

  It very hard to learn internals of h264, when nothing works.

  So, I have questions :

  1. What actual data inside mp4 ?
  2. What I must read to decode that data (I mean different annex-es)
  3. How to read stream and get decoded image (even with ffmpeg) from this "broken" raw stream ?

  UPDATE :

  It seems bug in ffmpeg :

  When I do double conversion :

           ffmpeg -ss 10 -i random_youtube_video.mp4 -frames 1 -c copy pic.mp4
  
           ffmpeg pic.mp4 -c copy pic.h264

  

  But when I convert file directly :

  ffmpeg -ss 10 -i random_youtube_video.mp4 -frames 1 -c copy pic.h264
  

  I have NALs signatures and one extra NAL unit. Other bytes are same (selected).

  This is bug ?

  UPDATE

  Not, this is not bug, U must use option -bsf h264_mp4toannexb to save stream as "Annex B" format (with prefixes)

• h264 inside AVI, MP4 and "Raw" h264 streams. Different format of NAL units

  6 octobre 2017, par bukkojot

  TL ;DR : I want to read raw h264 streams from AVI files, even broken/incomplete.

  Almost every document about h264 tells me that it consists of NAL packets. Okay. Almost everywhere told to me that the package should start with a signature like 00 00 01 or 00 00 00 01. For example, https://stackoverflow.com/a/18638298/8167678, https://stackoverflow.com/a/17625537/8167678

  The format of H.264 is that it’s made up of NAL Units, each starting
  with a start prefix of three bytes with the values 0x00, 0x00, 0x01
  and each unit has a different type depending on the value of the 4th
  byte right after these 3 starting bytes. One NAL Unit IS NOT one frame
  in the video, each frame is made up of a number of NAL Units.

  Okay.

  I downloaded random_youtube_video.mp4 and split one frame from it :

  ffmpeg -ss 10 -i random_youtube_video.mp4 -frames 1 -c copy pic.avi

  And got :
  
  Red part - this is part of AVI container, other - actual data.
  As you can see, here I have 00 00 24 A9 instead of 00 00 00 01

  This AVI file plays perfectly

  I do same for mp4 container :
  

  As you can see, here exact same bytes.
  This MP4 file plays perfectly

  I try to strip out raw data :
  ffmpeg -i pic.avi -c copy pic.h264
  

  This file can’t play in VLC or even ffmpeg, which produced this file, can’t parse it :
  

  I downloaded mp4 stream analyzer and got :
  

  MP4Box tells me :

   Cannot find H264 start code
  
   Error importing pic.h264: BitStream Not Compliant

  It very hard to learn internals of h264, when nothing works.

  So, I have questions :

  1. What actual data inside mp4 ?
  2. What I must read to decode that data (I mean different annex-es)
  3. How to read image and get decoded image (even with ffmpeg) from this "broken" raw stream ?

  UPDATE :

  It seems bug in ffmpeg :

  When I do double conversion :

           ffmpeg -ss 10 -i random_youtube_video.mp4 -frames 1 -c copy pic.mp4
  
           ffmpeg pic.mp4 -c copy pic.h264

  

  But when I convert file directly :

  ffmpeg -ss 10 -i random_youtube_video.mp4 -frames 1 -c copy pic.h264
  

  I have NALs signatures and one extra NAL unit. Other bytes are same (selected).

  This is bug ?