1 /*
2  * Copyright (C) 2016 The Android Open Source Project
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  *      http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 package com.google.android.exoplayer2.extractor.mp4;
17 
18 import com.google.android.exoplayer2.C;
19 import com.google.android.exoplayer2.util.Util;
20 
21 /**
22  * Rechunks fixed sample size media in which every sample is a key frame (e.g. uncompressed audio).
23  */
24 /* package */ final class FixedSampleSizeRechunker {
25 
26   /**
27    * The result of a rechunking operation.
28    */
29   public static final class Results {
30 
31     public final long[] offsets;
32     public final int[] sizes;
33     public final int maximumSize;
34     public final long[] timestamps;
35     public final int[] flags;
36     public final long duration;
37 
Results( long[] offsets, int[] sizes, int maximumSize, long[] timestamps, int[] flags, long duration)38     private Results(
39         long[] offsets,
40         int[] sizes,
41         int maximumSize,
42         long[] timestamps,
43         int[] flags,
44         long duration) {
45       this.offsets = offsets;
46       this.sizes = sizes;
47       this.maximumSize = maximumSize;
48       this.timestamps = timestamps;
49       this.flags = flags;
50       this.duration = duration;
51     }
52 
53   }
54 
55   /**
56    * Maximum number of bytes for each buffer in rechunked output.
57    */
58   private static final int MAX_SAMPLE_SIZE = 8 * 1024;
59 
60   /**
61    * Rechunk the given fixed sample size input to produce a new sequence of samples.
62    *
63    * @param fixedSampleSize Size in bytes of each sample.
64    * @param chunkOffsets Chunk offsets in the MP4 stream to rechunk.
65    * @param chunkSampleCounts Sample counts for each of the MP4 stream's chunks.
66    * @param timestampDeltaInTimeUnits Timestamp delta between each sample in time units.
67    */
rechunk(int fixedSampleSize, long[] chunkOffsets, int[] chunkSampleCounts, long timestampDeltaInTimeUnits)68   public static Results rechunk(int fixedSampleSize, long[] chunkOffsets, int[] chunkSampleCounts,
69       long timestampDeltaInTimeUnits) {
70     int maxSampleCount = MAX_SAMPLE_SIZE / fixedSampleSize;
71 
72     // Count the number of new, rechunked buffers.
73     int rechunkedSampleCount = 0;
74     for (int chunkSampleCount : chunkSampleCounts) {
75       rechunkedSampleCount += Util.ceilDivide(chunkSampleCount, maxSampleCount);
76     }
77 
78     long[] offsets = new long[rechunkedSampleCount];
79     int[] sizes = new int[rechunkedSampleCount];
80     int maximumSize = 0;
81     long[] timestamps = new long[rechunkedSampleCount];
82     int[] flags = new int[rechunkedSampleCount];
83 
84     int originalSampleIndex = 0;
85     int newSampleIndex = 0;
86     for (int chunkIndex = 0; chunkIndex < chunkSampleCounts.length; chunkIndex++) {
87       int chunkSamplesRemaining = chunkSampleCounts[chunkIndex];
88       long sampleOffset = chunkOffsets[chunkIndex];
89 
90       while (chunkSamplesRemaining > 0) {
91         int bufferSampleCount = Math.min(maxSampleCount, chunkSamplesRemaining);
92 
93         offsets[newSampleIndex] = sampleOffset;
94         sizes[newSampleIndex] = fixedSampleSize * bufferSampleCount;
95         maximumSize = Math.max(maximumSize, sizes[newSampleIndex]);
96         timestamps[newSampleIndex] = (timestampDeltaInTimeUnits * originalSampleIndex);
97         flags[newSampleIndex] = C.BUFFER_FLAG_KEY_FRAME;
98 
99         sampleOffset += sizes[newSampleIndex];
100         originalSampleIndex += bufferSampleCount;
101 
102         chunkSamplesRemaining -= bufferSampleCount;
103         newSampleIndex++;
104       }
105     }
106     long duration = timestampDeltaInTimeUnits * originalSampleIndex;
107 
108     return new Results(offsets, sizes, maximumSize, timestamps, flags, duration);
109   }
110 
FixedSampleSizeRechunker()111   private FixedSampleSizeRechunker() {
112     // Prevent instantiation.
113   }
114 }
115