morgan pushed to branch base-browser-128.8.0esr-14.5-1 at The Tor Project / Applications / Tor Browser

Commits: 2aa78353 by John Lin at 2025-03-10T14:20:42+00:00 Bug 1924070 - modify H.264 extradata to match sample conversion code. r=media-playback-reviewers,alwu

In AVC stream, NAL unit is represented with the length of unit data (NALUnitLength) followed by the actual unit data(NALUnit). The NALUnitLength field can be 1-4 bytes long and the size can be derived from the 'lengthSizeMinusOne' value recorded in extradata. H264ChangeMonitor.CheckForChange() reformats all input samples so that NALUnitLength will always be 4 bytes long while the original extradata is used during decoder creation earlier, so decoder won't be able to correctly parse converted samples if extradata is not modified accordingly.

Differential Revision: https://phabricator.services.mozilla.com/D239547 - - - - -

1 changed file:

- dom/media/platforms/wrappers/MediaChangeMonitor.cpp

Changes:

===================================== dom/media/platforms/wrappers/MediaChangeMonitor.cpp ===================================== @@ -42,6 +42,14 @@ class H264ChangeMonitor : public MediaChangeMonitor::CodecChangeMonitor { : mCurrentConfig(aInfo), mFullParsing(aFullParsing) { if (CanBeInstantiated()) { UpdateConfigFromExtraData(aInfo.mExtraData); + auto avcc = AVCCConfig::Parse(mCurrentConfig.mExtraData); + if (avcc.isOk() && avcc.unwrap().NALUSize() != 4) { + // `CheckForChange()` will use `AnnexB::ConvertSampleToAVCC()` to change + // NAL units into 4-byte. + // `AVCDecoderConfigurationRecord.lengthSizeMinusOne` in the config + // should be modified too. + mCurrentConfig.mExtraData->ReplaceElementAt(4, 0xfc | 3); + } } }

View it on GitLab: https://gitlab.torproject.org/tpo/applications/tor-browser/-/commit/2aa78353...