mp4緩衝播放

情景描述

    後臺上傳mp4文件到服務器，通過nginx代理靜態資源MP4把訪問地址參數提供給app。app用戶反應，視頻無法加載。或者加載過慢。（在chrome，firefox,360等衆多瀏覽器直接訪問mp4訪問地址都是秒播）

mp4文件格式

moov對於MP4來說，就是目錄，它是包含着mp4的元數據。moov模塊存放着如下信息
   1 視頻包括編碼等級、分辨率、色域、碼率、幀率、位深、時長等等……
   2 音頻又包括聲道、採樣率等音頻特有屬性

mdat:媒體數據容器。存放mp4大內容的地方。

加載快慢的原因是（元數據模塊的順序和使用的訪問方式）

1 秒播：chrome，firefox,360 很智能，如果讀取MP4文件，發現moov box不在文件前部，會直接讀取MP4的文件尾部，加載moov box
2 卡頓：Flash如果讀取MP4文件，發現moov box不在文件前部，不會直接讀取MP4的文件尾部去尋找moov box，所以Flash要等文件全部下載完，取到文件尾部的moov頭，纔可以正常播放。
3 流媒體服務器，即使moov在文件尾部 也會先發moov頭出去給CDN或用戶，相當於CDN回源，或者用戶回源請求到的MP4，已經是moov頭在文件頭部的了，雖然 這個時候 源站存儲的還是moov頭在文件尾部的MP4。

綜上所述：所以，如果安卓採用和flash一樣的機制來順序解析mp4文件，如果mp4文件的moov模塊在mdat後面。那麼就會造成卡頓！！！

解決辦法：

知道了mp4播放的原理，我們只要保證。moov在mdat前面解析就行了。ps：修改mp4文件大模塊的順序，是不會影響這個文件整體效果的。

方法1：部署流媒體服務器，給安卓提供流媒體的播放地址。不再採用http地址訪問MP4。（成本高，複雜，不考慮）
方法2：修改mp4文件的模塊順序。（修改mp4模塊順序的代碼，可百度，nice）
方法3：安卓端修改解析mp4的順序，先解析moov模塊。（不懂安卓，不考慮）

附：修改mp4文件模塊的代碼(百度不到我也不會選擇這個辦法對吧 https://blog.csdn.net/lzh838330255/article/details/53286430)

  package cc.ligu.mvc.common;
  import java.io.*;
  import java.nio.ByteBuffer;
  import java.nio.ByteOrder;
  import java.nio.channels.FileChannel;

  public class QtFastStart {
      public static boolean sDEBUG = false;

      private static void safeClose(Closeable closeable) {
          if (closeable != null) {
              try {
                  closeable.close();
              } catch (IOException e) {
                  printe(e, "Failed to close file: ");
              }
          }
      }

      /* package */
      static long uint32ToLong(int int32) {
          return int32 & 0x00000000ffffffffL;
      }

      /**
       * Ensures passed uint32 value in long can be represented as Java int.
       */
      /* package */
      static int uint32ToInt(int uint32) throws UnsupportedFileException {
          if (uint32 < 0) {
              throw new UnsupportedFileException("uint32 value is too large");
          }
          return uint32;
      }

      /**
       * Ensures passed uint32 value in long can be represented as Java int.
       */
      /* package */
      static int uint32ToInt(long uint32) throws UnsupportedFileException {
          if (uint32 > Integer.MAX_VALUE || uint32 < 0) {
              throw new UnsupportedFileException("uint32 value is too large");
          }
          return (int) uint32;
      }

      /**
       * Ensures passed uint64 value can be represented as Java long.
       */
      /* package */
      static long uint64ToLong(long uint64) throws UnsupportedFileException {
          if (uint64 < 0) throw new UnsupportedFileException("uint64 value is too large");
          return uint64;
      }

      private static int fourCcToInt(byte[] byteArray) {
          return ByteBuffer.wrap(byteArray).order(ByteOrder.BIG_ENDIAN).getInt();
      }

      private static void printf(String format, Object... args) {
          if (sDEBUG) System.err.println("QtFastStart: " + String.format(format, args));
      }

      private static void printe(Throwable e, String format, Object... args) {
          printf(format, args);
          if (sDEBUG) e.printStackTrace();
      }

      private static boolean readAndFill(FileChannel infile, ByteBuffer buffer) throws IOException {
          buffer.clear();
          int size = infile.read(buffer);
          buffer.flip();
          return size == buffer.capacity();
      }

      private static boolean readAndFill(FileChannel infile, ByteBuffer buffer, long position) throws IOException {
          buffer.clear();
          int size = infile.read(buffer, position);
          buffer.flip();
          return size == buffer.capacity();
      }

      /* top level atoms */
      private static final int FREE_ATOM = fourCcToInt(new byte[]{'f', 'r', 'e', 'e'});
      private static final int JUNK_ATOM = fourCcToInt(new byte[]{'j', 'u', 'n', 'k'});
      private static final int MDAT_ATOM = fourCcToInt(new byte[]{'m', 'd', 'a', 't'});
      private static final int MOOV_ATOM = fourCcToInt(new byte[]{'m', 'o', 'o', 'v'});
      private static final int PNOT_ATOM = fourCcToInt(new byte[]{'p', 'n', 'o', 't'});
      private static final int SKIP_ATOM = fourCcToInt(new byte[]{'s', 'k', 'i', 'p'});
      private static final int WIDE_ATOM = fourCcToInt(new byte[]{'w', 'i', 'd', 'e'});
      private static final int PICT_ATOM = fourCcToInt(new byte[]{'P', 'I', 'C', 'T'});
      private static final int FTYP_ATOM = fourCcToInt(new byte[]{'f', 't', 'y', 'p'});
      private static final int UUID_ATOM = fourCcToInt(new byte[]{'u', 'u', 'i', 'd'});

      private static final int CMOV_ATOM = fourCcToInt(new byte[]{'c', 'm', 'o', 'v'});
      private static final int STCO_ATOM = fourCcToInt(new byte[]{'s', 't', 'c', 'o'});
      private static final int CO64_ATOM = fourCcToInt(new byte[]{'c', 'o', '6', '4'});

      private static final int ATOM_PREAMBLE_SIZE = 8;

      public static boolean fastStart(InputStream in, FileOutputStream out) throws IOException, MalformedFileException, UnsupportedFileException {
          boolean ret = false;
          FileInputStream inStream = (FileInputStream) in;
          FileChannel infile = null;
          FileChannel outfile= null;
          try {
              infile = inStream.getChannel();
              outfile = out.getChannel();
              return ret = fastStartImpl(infile, outfile);
          } finally {
              if (!ret) {
                  infile.transferTo(0, infile.size(), outfile);//當轉換不成功時（正常是因文件小），直接copy.
  //                out.delete();
              }else{
  //                in.delete();
              }
              safeClose(inStream);
              safeClose(out);
          }
      }
      /**
       * @param in  Input file.
       * @param out Output file.
       * @return false if input file is already fast start.
       * @throws IOException
       */
      public static boolean fastStart(String in, String out) throws IOException, MalformedFileException, UnsupportedFileException {
          boolean ret = false;
          FileInputStream inStream = null;
          FileOutputStream outStream = null;
          FileChannel infile = null;
          FileChannel outfile= null;
          try {
              inStream = new FileInputStream(in);
              infile = inStream.getChannel();
              outStream = new FileOutputStream(out);
              outfile = outStream.getChannel();
              return ret = fastStartImpl(infile, outfile);
          } finally {
              if (!ret) {
                  infile.transferTo(0, infile.size(), outfile);//當轉換不成功時（正常是因文件小），直接copy.
  //                out.delete();
              }else{
  //                in.delete();
              }
              safeClose(inStream);
              safeClose(outStream);
          }
      }

      private static boolean fastStartImpl(FileChannel infile, FileChannel outfile) throws IOException, MalformedFileException, UnsupportedFileException {
          ByteBuffer atomBytes = ByteBuffer.allocate(ATOM_PREAMBLE_SIZE).order(ByteOrder.BIG_ENDIAN);
          int atomType = 0;
          long atomSize = 0; // uint64_t
          long lastOffset;
          ByteBuffer moovAtom;
          ByteBuffer ftypAtom = null;
          // uint64_t, but assuming it is in int32 range. It is reasonable as int max is around 2GB. Such large moov is unlikely, yet unallocatable :).
          int moovAtomSize;
          long startOffset = 0;
          System.out.println("QtFastStart------"+"開始");
          // traverse through the atoms in the file to make sure that 'moov' is at the end
          while (readAndFill(infile, atomBytes)) {
              atomSize = uint32ToLong(atomBytes.getInt()); // uint32
              atomType = atomBytes.getInt(); // representing uint32_t in signed int

              // keep ftyp atom
              if (atomType == FTYP_ATOM) {
                  int ftypAtomSize = uint32ToInt(atomSize); // XXX: assume in range of int32_t
                  ftypAtom = ByteBuffer.allocate(ftypAtomSize).order(ByteOrder.BIG_ENDIAN);
                  atomBytes.rewind();
                  ftypAtom.put(atomBytes);
                  if (infile.read(ftypAtom) < ftypAtomSize - ATOM_PREAMBLE_SIZE) break;
                  ftypAtom.flip();
                  startOffset = infile.position(); // after ftyp atom
                  System.out.println("QtFastStart---FTYP_ATOM---atomType:"+atomType);
                  System.out.println("QtFastStart---FTYP_ATOM---atomType:"+String.valueOf(infile.position()));
              } else {
  //                System.out.println("QtFastStart------atomType:"+atomType);
                  if (atomSize == 1) {
                      /* 64-bit special case */
                      atomBytes.clear();
                      if (!readAndFill(infile, atomBytes)) break;
                      atomSize = uint64ToLong(atomBytes.getLong()); // XXX: assume in range of int64_t
                      infile.position(infile.position() + atomSize - ATOM_PREAMBLE_SIZE * 2); // seek
                      System.out.println("QtFastStart--atomSize == 1----atomType:"+atomType);
                  } else {
                      infile.position(infile.position() + atomSize - ATOM_PREAMBLE_SIZE); // seek
                      System.out.println("QtFastStart--else----atomType:"+atomType);
                      System.out.println("QtFastStart--else----atomType:"+String.valueOf(infile.position() + atomSize - ATOM_PREAMBLE_SIZE));
                  }
              }
              if (sDEBUG) printf("%c%c%c%c %10d %d",
                      (atomType >> 24) & 255,
                      (atomType >> 16) & 255,
                      (atomType >> 8) & 255,
                      (atomType >> 0) & 255,
                      infile.position() - atomSize,
                      atomSize);
              if ((atomType != FREE_ATOM)
                      && (atomType != JUNK_ATOM)
                      && (atomType != MDAT_ATOM)
                      && (atomType != MOOV_ATOM)
                      && (atomType != PNOT_ATOM)
                      && (atomType != SKIP_ATOM)
                      && (atomType != WIDE_ATOM)
                      && (atomType != PICT_ATOM)
                      && (atomType != UUID_ATOM)
                      && (atomType != FTYP_ATOM)) {
                  printf("encountered non-QT top-level atom (is this a QuickTime file?)");
                  break;
              }

          /* The atom header is 8 (or 16 bytes), if the atom size (which
           * includes these 8 or 16 bytes) is less than that, we won't be
           * able to continue scanning sensibly after this atom, so break. */
              if (atomSize < 8)
                  break;
          }
          System.out.println("QtFastStart------"+"第一循環結束atomType:"+atomType);
          if (atomType != MOOV_ATOM) {
              printf("last atom in file was not a moov atom");
              return false;
          }
          // moov atom was, in fact, the last atom in the chunk; load the whole moov atom

          // atomSize is uint64, but for moov uint32 should be stored.
          // XXX: assuming moov atomSize <= max vaue of int32
          moovAtomSize = uint32ToInt(atomSize);
          lastOffset = infile.size() - moovAtomSize; // NOTE: assuming no extra data after moov, as qt-faststart.c
          moovAtom = ByteBuffer.allocate(moovAtomSize).order(ByteOrder.BIG_ENDIAN);
          if (!readAndFill(infile, moovAtom, lastOffset)) {
              throw new MalformedFileException("failed to read moov atom");
          }

          // this utility does not support compressed atoms yet, so disqualify files with compressed QT atoms
          if (moovAtom.getInt(12) == CMOV_ATOM) {
              throw new UnsupportedFileException("this utility does not support compressed moov atoms yet");
          }

          // crawl through the moov chunk in search of stco or co64 atoms
          while (moovAtom.remaining() >= 8) {
              int atomHead = moovAtom.position();
              atomType = moovAtom.getInt(atomHead + 4); // representing uint32_t in signed int
              if (!(atomType == STCO_ATOM || atomType == CO64_ATOM)) {
                  moovAtom.position(moovAtom.position() + 1);
                  continue;
              }
              atomSize = uint32ToLong(moovAtom.getInt(atomHead)); // uint32
              if (atomSize > moovAtom.remaining()) {
                  throw new MalformedFileException("bad atom size");
              }
              moovAtom.position(atomHead + 12); // skip size (4 bytes), type (4 bytes), version (1 byte) and flags (3 bytes)
              if (moovAtom.remaining() < 4) {
                  throw new MalformedFileException("malformed atom");
              }
              // uint32_t, but assuming moovAtomSize is in int32 range, so this will be in int32 range
              int offsetCount = uint32ToInt(moovAtom.getInt());
              if (atomType == STCO_ATOM) {
                  printf("patching stco atom...");
                  if (moovAtom.remaining() < offsetCount * 4) {
                      throw new MalformedFileException("bad atom size/element count");
                  }
                  for (int i = 0; i < offsetCount; i++) {
                      int currentOffset = moovAtom.getInt(moovAtom.position());
                      int newOffset = currentOffset + moovAtomSize; // calculate uint32 in int, bitwise addition
                      // current 0xffffffff => new 0x00000000 (actual >= 0x0000000100000000L)
                      if (currentOffset < 0 && newOffset >= 0) {
                          throw new UnsupportedFileException("This is bug in original qt-faststart.c: "
                                  + "stco atom should be extended to co64 atom as new offset value overflows uint32, "
                                  + "but is not implemented.");
                      }
                      moovAtom.putInt(newOffset);
                  }
              } else if (atomType == CO64_ATOM) {
                  printf("patching co64 atom...");
                  if (moovAtom.remaining() < offsetCount * 8) {
                      throw new MalformedFileException("bad atom size/element count");
                  }
                  for (int i = 0; i < offsetCount; i++) {
                      long currentOffset = moovAtom.getLong(moovAtom.position());
                      moovAtom.putLong(currentOffset + moovAtomSize); // calculate uint64 in long, bitwise addition
                  }
              }
          }
          infile.position(startOffset); // seek after ftyp atom

          if (ftypAtom != null) {
              // dump the same ftyp atom
              printf("writing ftyp atom...");
              ftypAtom.rewind();
              outfile.write(ftypAtom);
          }

          // dump the new moov atom
          printf("writing moov atom...");
          moovAtom.rewind();
          outfile.write(moovAtom);

          // copy the remainder of the infile, from offset 0 -> (lastOffset - startOffset) - 1
          printf("copying rest of file...");
          infile.transferTo(startOffset, lastOffset - startOffset, outfile);
          System.out.println("QtFastStart------"+"處理完成");
          return true;
      }

      public static class QtFastStartException extends Exception {
          private QtFastStartException(String detailMessage) {
              super(detailMessage);
          }
      }

      public static class MalformedFileException extends QtFastStartException {
          private MalformedFileException(String detailMessage) {
              super(detailMessage);
          }
      }

      public static class UnsupportedFileException extends QtFastStartException {
          private UnsupportedFileException(String detailMessage) {
              super(detailMessage);
          }
      }


      public static void main(String[] args) {
          try {
              String path = "C:\\Users\\shenyy\\Desktop\\待轉換視頻\\1540710345332.mp4";
              InputStream in = new FileInputStream(path);
              FileOutputStream out = new FileOutputStream(path+"_");
              boolean success = QtFastStart.fastStart(in, out);
          } catch (IOException e) {
              e.printStackTrace();
          } catch (MalformedFileException e) {
              e.printStackTrace();
          } catch (UnsupportedFileException e) {
              e.printStackTrace();
          }
      }

  }

附：視頻轉換前後的模塊順序對比 1前。2後

1

2

很明顯，同一個文件，模塊順序變了，使用flash播放，moov在前的明顯秒播。

效果

附 mp4文件詳細格式