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      1 /*
      2  * Copyright (C) 2010 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 
     17 package android.net.rtp;
     18 
     19 import java.util.Arrays;
     20 
     21 /**
     22  * This class defines a collection of audio codecs to be used with
     23  * {@link AudioStream}s. Their parameters are designed to be exchanged using
     24  * Session Description Protocol (SDP). Most of the values listed here can be
     25  * found in RFC 3551, while others are described in separated standards.
     26  *
     27  * <p>Few simple configurations are defined as public static instances for the
     28  * convenience of direct uses. More complicated ones could be obtained using
     29  * {@link #getCodec(int, String, String)}. For example, one can use the
     30  * following snippet to create a mode-1-only AMR codec.</p>
     31  * <pre>
     32  * AudioCodec codec = AudioCodec.getCodec(100, "AMR/8000", "mode-set=1");
     33  * </pre>
     34  *
     35  * @see AudioStream
     36  */
     37 public class AudioCodec {
     38     /**
     39      * The RTP payload type of the encoding.
     40      */
     41     public final int type;
     42 
     43     /**
     44      * The encoding parameters to be used in the corresponding SDP attribute.
     45      */
     46     public final String rtpmap;
     47 
     48     /**
     49      * The format parameters to be used in the corresponding SDP attribute.
     50      */
     51     public final String fmtp;
     52 
     53     /**
     54      * G.711 u-law audio codec.
     55      */
     56     public static final AudioCodec PCMU = new AudioCodec(0, "PCMU/8000", null);
     57 
     58     /**
     59      * G.711 a-law audio codec.
     60      */
     61     public static final AudioCodec PCMA = new AudioCodec(8, "PCMA/8000", null);
     62 
     63     /**
     64      * GSM Full-Rate audio codec, also known as GSM-FR, GSM 06.10, GSM, or
     65      * simply FR.
     66      */
     67     public static final AudioCodec GSM = new AudioCodec(3, "GSM/8000", null);
     68 
     69     /**
     70      * GSM Enhanced Full-Rate audio codec, also known as GSM-EFR, GSM 06.60, or
     71      * simply EFR.
     72      */
     73     public static final AudioCodec GSM_EFR = new AudioCodec(96, "GSM-EFR/8000", null);
     74 
     75     /**
     76      * Adaptive Multi-Rate narrowband audio codec, also known as AMR or AMR-NB.
     77      * Currently CRC, robust sorting, and interleaving are not supported. See
     78      * more details about these features in RFC 4867.
     79      */
     80     public static final AudioCodec AMR = new AudioCodec(97, "AMR/8000", null);
     81 
     82     private static final AudioCodec[] sCodecs = {GSM_EFR, AMR, GSM, PCMU, PCMA};
     83 
     84     private AudioCodec(int type, String rtpmap, String fmtp) {
     85         this.type = type;
     86         this.rtpmap = rtpmap;
     87         this.fmtp = fmtp;
     88     }
     89 
     90     /**
     91      * Returns system supported audio codecs.
     92      */
     93     public static AudioCodec[] getCodecs() {
     94         return Arrays.copyOf(sCodecs, sCodecs.length);
     95     }
     96 
     97     /**
     98      * Creates an AudioCodec according to the given configuration.
     99      *
    100      * @param type The payload type of the encoding defined in RTP/AVP.
    101      * @param rtpmap The encoding parameters specified in the corresponding SDP
    102      *     attribute, or null if it is not available.
    103      * @param fmtp The format parameters specified in the corresponding SDP
    104      *     attribute, or null if it is not available.
    105      * @return The configured AudioCodec or {@code null} if it is not supported.
    106      */
    107     public static AudioCodec getCodec(int type, String rtpmap, String fmtp) {
    108         if (type < 0 || type > 127) {
    109             return null;
    110         }
    111 
    112         AudioCodec hint = null;
    113         if (rtpmap != null) {
    114             String clue = rtpmap.trim().toUpperCase();
    115             for (AudioCodec codec : sCodecs) {
    116                 if (clue.startsWith(codec.rtpmap)) {
    117                     String channels = clue.substring(codec.rtpmap.length());
    118                     if (channels.length() == 0 || channels.equals("/1")) {
    119                         hint = codec;
    120                     }
    121                     break;
    122                 }
    123             }
    124         } else if (type < 96) {
    125             for (AudioCodec codec : sCodecs) {
    126                 if (type == codec.type) {
    127                     hint = codec;
    128                     rtpmap = codec.rtpmap;
    129                     break;
    130                 }
    131             }
    132         }
    133 
    134         if (hint == null) {
    135             return null;
    136         }
    137         if (hint == AMR && fmtp != null) {
    138             String clue = fmtp.toLowerCase();
    139             if (clue.contains("crc=1") || clue.contains("robust-sorting=1") ||
    140                     clue.contains("interleaving=")) {
    141                 return null;
    142             }
    143         }
    144         return new AudioCodec(type, rtpmap, fmtp);
    145     }
    146 }
    147