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• libavcodec on media entirely in memory

  11 janvier 2019, par Nick

  I’m dealing with small micro videos that exist entirely in memory (as a string). So far, I haven’t been able to get avcodec to properly decode h264 in this way.

  I tried a custom AVIOContext that operates on containerized media :

  struct Stream { char* str; size_t pos; size_t size; };
  
  
  
  static int ReadStream(void* opaque, uint8* buf, int buf_size) {
  
    Stream* strm = reinterpret_cast(opaque);
  
    int read = strm->size-strm->pos;
  
    read = read < buf_size ? read : buf_size;
  
    memcpy(buf, strm->str+sto-�>pos, read);
  
    memset(buf+read, 0, buf_size-read);
  
    strm->pos += read;
  
    return read;
  
  }
  
  
  
  static int64_t SeekStream(void *opaque, int64_t offset, int whence) {
  
    Stream* strm = reinterpret_cast(opaque);
  
    if (whence == AVSEEK_SIZE) {
  
      return strm->size;
  
    } else if (whence == SEEK_END) {
  
      strm->pos = strm->size;
  
    } else if (whence == SEEK_SET) {
  
      strm->pos = 0;
  
    }
  
    strm->pos += offset;
  
    return strm->pos;
  
  }
  
  
  
  int main(int argc, char *argv[]) {
  
    string content;
  
    GetContents("test.mp4", &content);
  
  
  
    avcodec_register_all();
  
  
  
    uint8* buff = (uint8*)malloc(4096 + AV_INPUT_BUFFER_PADDING_SIZE);
  
    Stream strm = { const_cast(content.data()), 0, content.size() };
  
    void* opaque = reinterpret_cast(&strm);
  
  
  
    AVFormatContext* fmtctx = avformat_alloc_context();
  
    AVIOContext* avctx = avio_alloc_context(buff, 4096, 0, opaque, &ReadStream, nullptr, &SeekStream);
  
    AVInputFormat* ifmt = av_find_input_format("mp4");
  
    AVDictionary* opts = nullptr;
  
  
  
    fmtctx->pb = avctx;
  
    avformat_open_input(&fmtctx, "", ifmt, &opts);
  
    avformat_find_stream_info(fmtctx, &opts);
  
  }

  But that always segfaults at find_stream_info.

  I also tried pre-demuxing the video stream into raw h264 and just sending the stream packets (e.g.) :

  int main(int argc, char *argv[]) {
  
    string content;
  
    GetContents("test.h264", &content);
  
    uint8* data = reinterpret_cast(const_cast(content.c_str()));
  
  
  
    avcodec_register_all();
  
  
  
    AVCodec* codec = avcodec_find_decoder(AV_CODEC_ID_H264);
  
    AVCodecContext* ctx = avcodec_alloc_context3(codec);
  
  
  
    ctx->width = 1080;
  
    ctx->height = 1920;
  
    avcodec_open2(ctx, codec, nullptr);
  
  
  
    AVPacket* pkt = av_packet_alloc();    
  
    AVFrame* frame = av_frame_alloc();
  
  
  
    pkt->data = data;
  
    pkt->size = 4096;
  
    avcodec_send_packet(ctx, pkt);
  
    data += 4096;
  
  }

  But that just gives a nondescript "error while decoding MB # #, bytestream #". Note that I’ve removed the error checking from the allocs, etc. to simplify the code, but I am checking to make sure everything is allocated and instantiated correctly.

  Any suggestions for where my misunderstanding or misuse of avcodec is ?

• Is there an efficient way to retrieve frames from a video in Android ?

  28 mars 2015, par Naveed

  I have an app which requires me to retrieve frames from a video and do some processing with them. However it seems like that the frame retrieval is very slow to the point where it is unacceptable. Sometimes it is taking upto 2.5 second to retrieve a single frame. I am using the MediaMetadataRetriever as most stackoverflow questions suggested. However the performance is very bad. Here is what I have :

     private List<bitmap> retrieveFrames() {
  
  
  
          MediaMetadataRetriever fmmr = new MediaMetadataRetriever();
  
          fmmr.setDataSource("/path/to/some/video.mp4");
  
          String strLength = fmmr.extractMetadata(MediaMetadataRetriever.METADATA_KEY_DURATION);
  
          long milliSecs = Long.parseLong(strLength);
  
          long microSecLength = milliSecs * 1000;
  
  
  
          Log.d("TAG", "length: " + microSecLength);
  
          long one_sec = 1000000; // one sec in micro seconds
  
  
  
          ArrayList<bitmap> frames = new ArrayList&lt;>();
  
          int j = 0;
  
          for (int i = 0; i &lt; microSecLength; i += (one_sec / 5)) {
  
              long time = System.currentTimeMillis();
  
              Bitmap frame = fmmr.getFrameAtTime(i, MediaMetadataRetriever.OPTION_CLOSEST);
  
              j++;
  
              Log.d("TAG", "Frame number: " + j + " Time taken: " + (System.currentTimeMillis() - time));
  
              // commented out because each frame would be written to disk instead of holding them in memory
  
              //  frames.add(frame);
  
          }
  
          fmmr.release();
  
          return frames;
  
      }
  
  </bitmap></bitmap>

  The above will logs :

  03-26 21:49:29.781  13213-13239/com.example.naveed.myapplication D/TAG﹕ length: 4949000
  
  03-26 21:49:30.187  13213-13239/com.example.naveed.myapplication D/TAG﹕ Frame number: 1 Time taken: 406
  
  03-26 21:49:30.779  13213-13239/com.example.naveed.myapplication D/TAG﹕ Frame number: 2 Time taken: 592
  
  03-26 21:49:31.578  13213-13239/com.example.naveed.myapplication D/TAG﹕ Frame number: 3 Time taken: 799
  
  03-26 21:49:32.632  13213-13239/com.example.naveed.myapplication D/TAG﹕ Frame number: 4 Time taken: 1054
  
  03-26 21:49:33.895  13213-13239/com.example.naveed.myapplication D/TAG﹕ Frame number: 5 Time taken: 1262
  
  03-26 21:49:35.382  13213-13239/com.example.naveed.myapplication D/TAG﹕ Frame number: 6 Time taken: 1486
  
  03-26 21:49:37.128  13213-13239/com.example.naveed.myapplication D/TAG﹕ Frame number: 7 Time taken: 1746
  
  03-26 21:49:39.077  13213-13239/com.example.naveed.myapplication D/TAG﹕ Frame number: 8 Time taken: 1948
  
  03-26 21:49:41.287  13213-13239/com.example.naveed.myapplication D/TAG﹕ Frame number: 9 Time taken: 2210
  
  03-26 21:49:43.717  13213-13239/com.example.naveed.myapplication D/TAG﹕ Frame number: 10 Time taken: 2429
  
  03-26 21:49:44.093  13213-13239/com.example.naveed.myapplication D/TAG﹕ Frame number: 11 Time taken: 376
  
  03-26 21:49:44.707  13213-13239/com.example.naveed.myapplication D/TAG﹕ Frame number: 12 Time taken: 614
  
  03-26 21:49:45.539  13213-13239/com.example.naveed.myapplication D/TAG﹕ Frame number: 13 Time taken: 831
  
  03-26 21:49:46.597  13213-13239/com.example.naveed.myapplication D/TAG﹕ Frame number: 14 Time taken: 1057
  
  03-26 21:49:47.875  13213-13239/com.example.naveed.myapplication D/TAG﹕ Frame number: 15 Time taken: 1278
  
  03-26 21:49:49.384  13213-13239/com.example.naveed.myapplication D/TAG﹕ Frame number: 16 Time taken: 1508
  
  03-26 21:49:51.112  13213-13239/com.example.naveed.myapplication D/TAG﹕ Frame number: 17 Time taken: 1728
  
  03-26 21:49:53.096  13213-13239/com.example.naveed.myapplication D/TAG﹕ Frame number: 18 Time taken: 1983
  
  03-26 21:49:55.315  13213-13239/com.example.naveed.myapplication D/TAG﹕ Frame number: 19 Time taken: 2218
  
  03-26 21:49:57.711  13213-13239/com.example.naveed.myapplication D/TAG﹕ Frame number: 20 Time taken: 2396
  
  03-26 21:49:58.065  13213-13239/com.example.naveed.myapplication D/TAG﹕ Frame number: 21 Time taken: 354
  
  03-26 21:49:58.640  13213-13239/com.example.naveed.myapplication D/TAG﹕ Frame number: 22 Time taken: 574
  
  03-26 21:49:59.369  13213-13239/com.example.naveed.myapplication D/TAG﹕ Frame number: 23 Time taken: 728
  
  03-26 21:50:00.112  13213-13239/com.example.naveed.myapplication D/TAG﹕ Frame number: 24 Time taken: 742
  
  03-26 21:50:00.834  13213-13239/com.example.naveed.myapplication D/TAG﹕ Frame number: 25 Time taken: 721

  As you can see from above, it is taking about 18 - 25 sec to retrieve 25 frames from a 4 sec long video.

  I have also tried this which uses FFmpeg underneath to do the same. I am not sure how well this library is implemented but it only improves the over all performance by a couple of seconds meaning it takes about 15-20 sec to do the same.

  So my question is : is there a way to do it quicker ? My friend has an iOS app where he does something similar but it only takes couple of seconds and he is grabbing even more frames however he is not sure how to do it on android.

  Is there anything on android that would speed up the process. Am I approaching this wrong ?

  The end goal is to stitch those frames together into a gif.

• Compiling ffmpeg for iOS and gas-preprocessor.pl

  16 mai 2017, par user500

  I want to compile ffmpeg for iOS. I did it a few times before. But now I’m on clean new Mavericks and on configure I’m always getting

  Configured with: --prefix=/Applications/Xcode.app/Contents/Developer/usr --with-gxx-include-dir=/usr/include/c++/4.2.1
  
  Configured with: --prefix=/Applications/Xcode.app/Contents/Developer/usr --with-gxx-include-dir=/usr/include/c++/4.2.1
  
  GNU assembler not found, install gas-preprocessor
  
  
  
  If you think configure made a mistake, make sure you are using the latest
  
  version from Git.  If the latest version fails, report the problem to the
  
  ffmpeg-user@ffmpeg.org mailing list or IRC #ffmpeg on irc.freenode.net.
  
  Include the log file "config.log" produced by configure as this will help
  
  solving the problem.

  I have current Xcode installed. Also brews. And current gas-preprocessor.pl (https://github.com/yuvi/gas-preprocessor) in usr/bin and also in usr/local/bin.

  ---

  On perl /usr/bin/gas-preprocessor.pl gcc I’m getting Unrecognized input filetype at /usr/bin/gas-preprocessor.pl line 33.

  ---

  This config works :

  ./configure \
  
  --extra-cflags='-arch arm64 -mios-version-min=7.0 -mthumb' \
  
  --extra-ldflags='-arch arm64 -mios-version-min=7.0' \
  
  --enable-cross-compile \
  
  --arch=arm64 \
  
  --target-os=darwin \
  
  --cc=/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang \
  
  --sysroot=/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS7.0.sdk \
  
  --prefix=arm64 \
  
  --disable-doc \
  
  --disable-shared \
  
  --disable-everything \
  
  --enable-static \
  
  --enable-pic \
  
  --disable-muxers \
  
  --enable-muxer=flv \
  
  --disable-demuxers \
  
  --enable-demuxer=h264 \
  
  --enable-demuxer=pcm_s16le \
  
  --disable-devices \
  
  --disable-parsers \
  
  --enable-parser=h264 \
  
  --disable-encoders \
  
  --enable-encoder=aac \
  
  --disable-decoders \
  
  --enable-decoder=h264 \
  
  --enable-decoder=pcm_s16le \
  
  --disable-protocols \
  
  --enable-protocol=rtmp \
  
  --disable-filters \
  
  --disable-bsfs

  ---

  This config throws error above (GNU assembler not found, install gas-preprocessor) :

  ./configure \
  
  --cpu=cortex-a8 \
  
  --extra-cflags='-arch armv7 -mios-version-min=7.0 -mthumb' \
  
  --extra-ldflags='-arch armv7 -mios-version-min=7.0' \
  
  --enable-cross-compile \
  
  --arch=armv7 \
  
  --target-os=darwin \
  
  --cc=/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang \
  
  --sysroot=/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS7.0.sdk \
  
  --prefix=armv7 \
  
  --disable-doc \
  
  --disable-shared \
  
  --disable-everything \
  
  --enable-static \
  
  --enable-pic \
  
  --disable-muxers \
  
  --enable-muxer=flv \
  
  --disable-demuxers \
  
  --enable-demuxer=h264 \
  
  --enable-demuxer=pcm_s16le \
  
  --disable-devices \
  
  --disable-parsers \
  
  --enable-parser=h264 \
  
  --disable-encoders \
  
  --enable-encoder=aac \
  
  --disable-decoders \
  
  --enable-decoder=h264 \
  
  --enable-decoder=pcm_s16le \
  
  --disable-protocols \
  
  --enable-protocol=rtmp \
  
  --disable-filters \
  
  --disable-bsfs