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Some wording and layout changes:
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- Reworded 'audio silence' message format for more clarity.
- Changed page layout to better support .pdf export.
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@slozben
slozben committed May 29, 2024
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53 changes: 29 additions & 24 deletions docs/enhanced/enhanced-rtmp-v2.md
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Expand Up @@ -35,7 +35,7 @@

**Author**: Slavik Lozben (Veovera Software Organization)(VSO) \
**Contributors**: Adobe, Google, Twitch, Jean-Baptiste Kempf (FFmpeg, VideoLAN), pkv (OBS), Dennis Sädtler (OBS), Xavier Hallade (Intel Corporation), Luxoft, SplitmediaLabs Limited (XSplit), Craig Barberich (VSO), Michael Thornburgh \
**Status**: **v2-2024-05-24-a1**
**Status**: **v2-2024-05-29-a1**

## Alpha Version Disclaimer for Enhanced RTMP v\* Specification

Expand Down Expand Up @@ -590,29 +590,30 @@ Table: Extended AudioTagHeader
¦// process ExAudioTagHeader ¦ SequenceStart = 0, ¦
¦// ¦ CodedFrames = 1, ¦
¦processAudioBody = false ¦ ¦
¦if (soundFormat == SoundFormat.ExHeader) { ¦ // RTMP includes a previously undocumented 'audio silence' message. This ¦
¦ processAudioBody = true ¦ // silence message is identified when an audio message contains a zero ¦
¦ ¦ // payload, indicating a period of silence. The action to take after ¦
¦ // The UB[4] bits are interpreted as AudioPacketType ¦ // receiving a silence message is system dependent. The semantics of the ¦
¦ // instead of sound rate, size and type ¦ // silence message in the Flash Media playback and timing model are as ¦
¦ audioPacketType = UB[4] as AudioPacketType ¦ // follows: ¦
¦ ¦ // ¦
¦ if (audioPacketType == AudioPacketType.Multitrack) { ¦ // - Ensure all buffered audio data is played out before entering the ¦
¦ isAudioMultitrack = true; ¦ // silence period: ¦
¦ audioMultitrackType = UB[4] as AvMultitrackType ¦ // Make sure that any audio data currently in the buffer is fully ¦
¦ ¦ // processed and played. This ensures a clean transition into the ¦
¦ // Fetch AudioPacketType for all audio tracks in the audio message. ¦ // silence period without cutting off any audio. ¦
¦ // This fetch MUST not result in a AudioPacketType.Multitrack ¦ // ¦
¦ audioPacketType = UB[4] as AudioPacketType ¦ // - After playing all buffered audio data, flush the audio decoder: ¦
¦ ¦ // Clear the audio decoder to reset its state and prepare it for new ¦
¦ if (audioMultitrackType != AvMultitrackType.ManyTracksManyCodecs) { ¦ // input after the silence period. ¦
¦ // The tracks are encoded with the same codec. Fetch the FOURCC for them ¦ // ¦
¦ audioFourCc = FOURCC as AudioFourCc ¦ // - During the silence period, the audio clock can't be used as the ¦
¦ } ¦ // master clock for synchronizing playback: ¦
¦ } else { ¦ // Switch to using the system's wall-clock time to maintain the correct ¦
¦ audioFourCc = FOURCC as AudioFourCc ¦ // timing for video and other data streams. ¦
¦ } ¦ // ¦
¦} ¦ // - Don't wait for audio frames for synchronized A+V playback: ¦
¦if (soundFormat == SoundFormat.ExHeader) { ¦ // RTMP includes a previously undocumented 'audio silence' message. ¦
¦ processAudioBody = true ¦ // This silence message is identified when an audio message contains ¦
¦ ¦ // a zero-length payload, or more precisely, an empty audio message ¦
¦ // The UB[4] bits are interpreted as AudioPacketType ¦ // without an AudioTagHeader, indicating a period of silence. The ¦
¦ // instead of sound rate, size and type ¦ // action to take after receiving a silence message is system ¦
¦ audioPacketType = UB[4] as AudioPacketType ¦ // dependent. The semantics of the silence message in the Flash ¦
¦ ¦ // Media playback and timing model are as follows: ¦
¦ if (audioPacketType == AudioPacketType.Multitrack) { ¦ // ¦
¦ isAudioMultitrack = true; ¦ // - Ensure all buffered audio data is played out before entering the ¦
¦ audioMultitrackType = UB[4] as AvMultitrackType ¦ // silence period: ¦
¦ ¦ // Make sure that any audio data currently in the buffer is fully ¦
¦ // Fetch AudioPacketType for all audio tracks in the audio message. ¦ // processed and played. This ensures a clean transition into the ¦
¦ // This fetch MUST not result in a AudioPacketType.Multitrack ¦ // silence period without cutting off any audio. ¦
¦ audioPacketType = UB[4] as AudioPacketType ¦ // ¦
¦ ¦ // - After playing all buffered audio data, flush the audio decoder: ¦
¦ if (audioMultitrackType != AvMultitrackType.ManyTracksManyCodecs) { ¦ // Clear the audio decoder to reset its state and prepare it for new ¦
¦ // The tracks are encoded with the same codec. Fetch the FOURCC for them ¦ // input after the silence period. ¦
¦ audioFourCc = FOURCC as AudioFourCc ¦ // ¦
¦ } ¦ // - During the silence period, the audio clock can't be used as the ¦
¦ } else { ¦ // master clock for synchronizing playback: ¦
¦ audioFourCc = FOURCC as AudioFourCc ¦ // Switch to using the system's wall-clock time to maintain the correct ¦
¦ } ¦ // timing for video and other data streams. ¦
¦} ¦ // ¦
¦ ¦ // - Don't wait for audio frames for synchronized A+V playback: ¦
¦ ¦ // Normally, audio frames drive the synchronization of audio and video ¦
¦ ¦ // (A/V) playback. During the silence period, playback should not stall ¦
¦ ¦ // waiting for audio frames. Video and other data streams should ¦
Expand Down Expand Up @@ -1523,4 +1524,8 @@ W3C, "WebCodecs" \
+----------------------+----------------------------------------------------------------------------------------+
¦ v2-2024-05-24-a1 ¦ 1. Fixed a bug in pseudocode when parsing FLAC sequence header. ¦
+----------------------+----------------------------------------------------------------------------------------+
¦ v2-2024-05-28-a1 ¦ 1. Reworded 'audio silence' message format for more clarity. ¦
+----------------------+----------------------------------------------------------------------------------------+
¦ v2-2024-05-29-a1 ¦ 1. Changed page layout to better support .pdf export. No actual spec changes. ¦
+----------------------+----------------------------------------------------------------------------------------+
```
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