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Why

GB/T 28181 platforms carry video as an MPEG-2 program stream over RTP, and OpenIPC cameras can now send SVAC 3.0 that way. FFmpeg's MPEG-PS demuxer did not know SVAC's stream type, so it could not read such a capture.

What

• 0003-avformat-mpeg-read-SVAC-video-from-a-GB-T-28181-program-stream.patch: maps stream_type 0x80 in the program stream map to AV_CODEC_ID_SVAC3. It applies only on a video stream id (0xE0–0xEF), because 0x80 is user-private in ISO/IEC 13818-1. The demuxer already sets full parsing, so the SVAC3 parser applies unchanged.
• ffmpeg/ps_write.py: an independent program-stream writer:
  • one pack per access unit;
  • a system header and map on units with an SPS or random-access patch;
  • PES packets split at the 16-bit length, with the PTS on the first.
• ffmpeg/ps_check.sh: writes every corpus stream with it, reads it back with -f mpeg, and checks against the golden framemd5. It runs as a new CI step; the CI FFmpeg build adds the mpegps demuxer.
• ffmpeg/README.md: documents the patch order and the program-stream notes.

Verified

• All 3 patches apply in order to a clean n9.0.2.
• All 8 corpus streams are bit-exact through ps_write.py → -f mpeg, SMART_P and multi-patch streams included.
• A program stream captured from a camera's RTSP PS/90000 session (its RTP payloads concatenated) decodes with -f mpeg: 240 frames at 1920x1080, the same count libsvac3d gives on the extracted elementary stream.

FFmpeg has no RTP depacketizer for PS/90000 itself; that is outside this repo's patches.

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PR Summary by Qodo

Read SVAC 3.0 from GB/T 28181 MPEG program streams

✨ Enhancement 🧪 Tests 🕐 20-40 Minutes

AI Description

• Recognize SVAC 3.0 in GB/T 28181 program streams without treating every private stream as SVAC.
• Generate program streams from the corpus and verify decoded frames against golden hashes in CI.
• Document patch order, program-stream playback, and the unsupported PS/90000 RTP transport.

Diagram

graph TD
  A["SVAC corpus"] --> B["PS writer"] --> C["Program stream"] --> D["MPEG-PS demuxer"] --> E["SVAC parser decoder"] --> F["Frame hash check"]
  G["Golden hashes"] --> F

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High-Level Assessment

The following are alternative approaches to this PR:

1. Validate SVAC payload before assigning the codec

• ➕ Reduces misclassification of other private 0x80 video streams.
• ➖ Adds probing complexity and may fail when reading from the middle of a stream.

2. Add a GB/T-specific program-stream demuxer

• ➕ Keeps the private stream-type interpretation separate from generic MPEG-PS handling.
• ➖ Duplicates established program-stream parsing for a narrow codec-mapping change.

Recommendation: Use the existing MPEG-PS demuxer and video-stream-ID guard as proposed; it is the smallest change that enables the documented captures. Revisit payload validation if interoperability with other private 0x80 video streams becomes necessary.

Files changed (5) +188 / -3

Enhancement (1) +46 / -0

0003-avformat-mpeg-read-SVAC-video-from-a-GB-T-28181-program-stream.patchMap GB/T 28181 program-stream video to SVAC3 +46/-0

Map GB/T 28181 program-stream video to SVAC3

• Adds the 0x80 stream-type definition and maps it to AV_CODEC_ID_SVAC3 in FFmpeg's MPEG-PS demuxer only for video stream IDs 0xE0–0xEF.

ffmpeg/0003-avformat-mpeg-read-SVAC-video-from-a-GB-T-28181-program-stream.patch

Tests (2) +120 / -0

ps_check.shCheck program-stream decoding against golden frame hashes +23/-0

Check program-stream decoding against golden frame hashes

• Wraps each matching corpus stream as a program stream, decodes it with FFmpeg's MPEG demuxer, and compares its framemd5 output with the existing golden result.

ffmpeg/ps_check.sh

ps_write.pyGenerate MPEG-2 program-stream fixtures from SVAC access units +97/-0

Generate MPEG-2 program-stream fixtures from SVAC access units

• Writes packs, headers, stream maps, timestamps, and length-bounded PES packets from the existing SVAC access-unit grouping. This provides an independent input generator for the demuxer regression check.

ffmpeg/ps_write.py

Documentation (1) +19 / -2

README.mdDocument program-stream support and verification +19/-2

Document program-stream support and verification

• Lists the third FFmpeg patch, describes the new corpus check, and explains playback of saved GB/T 28181 program streams. It notes that FFmpeg does not depacketize PS/90000 RTP.

ffmpeg/README.md

Other (1) +3 / -1

ci.ymlBuild MPEG-PS support and run the program-stream regression check +3/-1

Build MPEG-PS support and run the program-stream regression check

• Enables the mpegps demuxer in the minimal FFmpeg build and adds a CI step that runs the new corpus round-trip check.

.github/workflows/ci.yml

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Code Review by Qodo

🐞 Bugs (0) 📘 Rule violations (0) 📎 Requirement gaps (0)

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