Add support for RTSP PCM/WAV and G711/WAV

[basantwanishraddha]

Added PCM RTP packet reader and added support for PCM 8 bit,
16 bit, ALAW and MULAW playback through RTSP.

Change-Id: If0a187b55faa89850a159e17eae28358d6634799

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[claincly]

LG w/ nits, will fix in our internal processes.

[claincly]

Merged internally. The issue will be marked as merged automatically when we do a push. Thanks for the contribution!

[claincly]

Question: how did you test the PCM streams? Especially for PCMU, they have static payload types. Did you manage to generate a dynamic payload type for PCMU?

[claincly]

I tried to play this media using a local live555, and it didn't work. The cause is you are not handling static payload types. And even after I hardcoded the format (PCM L16, 44100Hz, 1 channel), the audio did not play.

[claincly]

This is the diff I used:

--- a/src/main/java/androidx/media3/exoplayer/rtsp/MediaDescription.java
+++ b/src/main/java/androidx/media3/exoplayer/rtsp/MediaDescription.java
@@ -105,6 +105,14 @@ import java.util.HashMap;
 
   /** Builder class for {@link MediaDescription}. */
   public static final class Builder {
+
+    /** RTPMAP attribute format: {@code <payloadType> <mediaEncoding>/<clockRate>/<channelCount>}. */
+    private static final String RTP_MAP_ATTR_AUDIO_FMT = "%d %s/%d/%d";
+    private static final int RTP_STATIC_PAYLOAD_TYPE_PCMU = 0;
+    private static final int RTP_STATIC_PAYLOAD_TYPE_PCMA = 8;
+    private static final int RTP_STATIC_PAYLOAD_TYPE_L16_STEREO = 10;
+    private static final int RTP_STATIC_PAYLOAD_TYPE_L16_MONO = 11;
+
     private final String mediaType;
     private final int port;
     private final String transportProtocol;
@@ -199,15 +207,52 @@ import java.util.HashMap;
      */
     public MediaDescription build() {
       try {
-        // rtpmap attribute is mandatory in RTSP (RFC2326 Section C.1.3).
-        checkState(attributes.containsKey(ATTR_RTPMAP));
         RtpMapAttribute rtpMapAttribute =
-            RtpMapAttribute.parse(castNonNull(attributes.get(ATTR_RTPMAP)));
+            attributes.containsKey(ATTR_RTPMAP)
+            ? RtpMapAttribute.parse(castNonNull(attributes.get(ATTR_RTPMAP)))
+            : RtpMapAttribute.parse(getRtpMapStringByPayloadType(payloadType));
         return new MediaDescription(this, ImmutableMap.copyOf(attributes), rtpMapAttribute);
       } catch (ParserException e) {
         throw new IllegalStateException(e);
       }
     }
+
+    private static String getRtpMapStringByPayloadType(int rtpPayloadType) {
+      checkArgument(rtpPayloadType < 96);
+
+      switch (rtpPayloadType) {
+        case RTP_STATIC_PAYLOAD_TYPE_PCMU:
+          return Util.formatInvariant(
+              RTP_MAP_ATTR_AUDIO_FMT,
+              /* payloadType= */ 0,
+              /* mediaEncoding= */ "PCMU",
+              /* clockRate= */ 8_000,
+              /* channelCount= */ 1);
+        case RTP_STATIC_PAYLOAD_TYPE_PCMA:
+          return Util.formatInvariant(
+              RTP_MAP_ATTR_AUDIO_FMT,
+              /* payloadType= */ 8,
+              /* mediaEncoding= */ "PCMA",
+              /* clockRate= */ 8_000,
+              /* channelCount= */ 1);
+        case RTP_STATIC_PAYLOAD_TYPE_L16_STEREO:
+          return Util.formatInvariant(
+              RTP_MAP_ATTR_AUDIO_FMT,
+              /* payloadType= */ 10,
+              /* mediaEncoding= */ "L16",
+              /* clockRate= */ 44_100,
+              /* channelCount= */ 2);
+        case RTP_STATIC_PAYLOAD_TYPE_L16_MONO:
+          return Util.formatInvariant(
+              RTP_MAP_ATTR_AUDIO_FMT,
+              /* payloadType= */ 11,
+              /* mediaEncoding= */ "L16",
+              /* clockRate= */ 44_100,
+              /* channelCount= */ 1);
+        default:
+          throw new IllegalStateException("Unsupported static paylod type " + rtpPayloadType);
+      }
+    }
   }
 
   /** The media types allowed in a SDP media description. */

Edit: I noticed the test clip is little-endian signed PCM, I edited this and still no good.

media/libraries/exoplayer_rtsp/src/main/java/androidx/media3/exoplayer/rtsp/RtpPayloadFormat.java

Line 119 in f8f1a4d

: C.ENCODING_PCM_16BIT_BIG_ENDIAN;

[basantwanishraddha]

The test stream that you have shared, I wasn't able to run it on VLC player as well. (Used live555 server)
I tried debugging the behavior on exoplayer, but it never reaches the onDescribeResponseReceived.
So the test stream seems to be the cause of issue.
In the case of PCM Reader we are using a WAV container, so we receive dynamic payload.
This is the audio clip that we have used to validate the PCM_MULAW mediaType.

[claincly]

Maybe you have used an old version of VLC/live555? My live555 binary (mac) works with the audio file I provided. if you want to have a try
l5.zip.

I'll try your clip.

That said, it's questionable to only support dynamic payload type as PCM audio streams can and are being served with static payload type.

[claincly]

Re-uploading the audio file
pcm.wav.zip

[basantwanishraddha]

I am able to play the audio file on exoplayer, after applying the diff you have shared.
No other change was required, setting it to big endian 16 bit is correct since live555 server converts little endian to big endian before streaming. (link)
Let us know if you are able to play on exoplayer after resetting it to 'Big endian 16 bit'.