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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  * @hide
     37  */
     38 public class AudioCodec {
     39     /**
     40      * The RTP payload type of the encoding.
     41      */
     42     public final int type;
     43 
     44     /**
     45      * The encoding parameters to be used in the corresponding SDP attribute.
     46      */
     47     public final String rtpmap;
     48 
     49     /**
     50      * The format parameters to be used in the corresponding SDP attribute.
     51      */
     52     public final String fmtp;
     53 
     54     /**
     55      * G.711 u-law audio codec.
     56      */
     57     public static final AudioCodec PCMU = new AudioCodec(0, "PCMU/8000", null);
     58 
     59     /**
     60      * G.711 a-law audio codec.
     61      */
     62     public static final AudioCodec PCMA = new AudioCodec(8, "PCMA/8000", null);
     63 
     64     /**
     65      * GSM Full-Rate audio codec, also known as GSM-FR, GSM 06.10, GSM, or
     66      * simply FR.
     67      */
     68     public static final AudioCodec GSM = new AudioCodec(3, "GSM/8000", null);
     69 
     70     /**
     71      * GSM Enhanced Full-Rate audio codec, also known as GSM-EFR, GSM 06.60, or
     72      * simply EFR.
     73      */
     74     public static final AudioCodec GSM_EFR = new AudioCodec(96, "GSM-EFR/8000", null);
     75 
     76     /**
     77      * Adaptive Multi-Rate narrowband audio codec, also known as AMR or AMR-NB.
     78      * Currently CRC, robust sorting, and interleaving are not supported. See
     79      * more details about these features in RFC 4867.
     80      */
     81     public static final AudioCodec AMR = new AudioCodec(97, "AMR/8000", null);
     82 
     83     private static final AudioCodec[] sCodecs = {GSM_EFR, AMR, GSM, PCMU, PCMA};
     84 
     85     private AudioCodec(int type, String rtpmap, String fmtp) {
     86         this.type = type;
     87         this.rtpmap = rtpmap;
     88         this.fmtp = fmtp;
     89     }
     90 
     91     /**
     92      * Returns system supported audio codecs.
     93      */
     94     public static AudioCodec[] getCodecs() {
     95         return Arrays.copyOf(sCodecs, sCodecs.length);
     96     }
     97 
     98     /**
     99      * Creates an AudioCodec according to the given configuration.
    100      *
    101      * @param type The payload type of the encoding defined in RTP/AVP.
    102      * @param rtpmap The encoding parameters specified in the corresponding SDP
    103      *     attribute, or null if it is not available.
    104      * @param fmtp The format parameters specified in the corresponding SDP
    105      *     attribute, or null if it is not available.
    106      * @return The configured AudioCodec or {@code null} if it is not supported.
    107      */
    108     public static AudioCodec getCodec(int type, String rtpmap, String fmtp) {
    109         if (type < 0 || type > 127) {
    110             return null;
    111         }
    112 
    113         AudioCodec hint = null;
    114         if (rtpmap != null) {
    115             String clue = rtpmap.trim().toUpperCase();
    116             for (AudioCodec codec : sCodecs) {
    117                 if (clue.startsWith(codec.rtpmap)) {
    118                     String channels = clue.substring(codec.rtpmap.length());
    119                     if (channels.length() == 0 || channels.equals("/1")) {
    120                         hint = codec;
    121                     }
    122                     break;
    123                 }
    124             }
    125         } else if (type < 96) {
    126             for (AudioCodec codec : sCodecs) {
    127                 if (type == codec.type) {
    128                     hint = codec;
    129                     rtpmap = codec.rtpmap;
    130                     break;
    131                 }
    132             }
    133         }
    134 
    135         if (hint == null) {
    136             return null;
    137         }
    138         if (hint == AMR && fmtp != null) {
    139             String clue = fmtp.toLowerCase();
    140             if (clue.contains("crc=1") || clue.contains("robust-sorting=1") ||
    141                     clue.contains("interleaving=")) {
    142                 return null;
    143             }
    144         }
    145         return new AudioCodec(type, rtpmap, fmtp);
    146     }
    147 }
    148