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The prior algorithm summed up all Opus frame's number of samples and calculated the expected timestamp from there. That expected timestamp was compared to the Ogg page's granule position, and the discard padding was calculated from that. This lead to problems in several cases: 1. When the first packet's granule position was bigger than the number of samples in the Opus frame, the specs say that the first sample's timestamp is positive in that case. mkvmerge was wrongfully using 0 as the timestamp and thought discard padding was needed in such a case. 2. When the first packet's granule position was smaller than the number of samples in the Opus frame (meaning the first sample's timestamp was negative), a technically invalid bitstream, mkvmerge was wrongfully forcing the first packet's timestamp up to 0 and inserting discard padding elements all over the place as its internal calculations got confused. The new algorithm bases the calculation on the last known granule position special-casing for certain Ogg packet numbers: 1. For the first Ogg page the timestamps of all packets is calculated by subtracting each packet's number of samples from the page's granule position in reverse order. This may result in the first packet's timestamp being positive, which mkvmerge now preserves. mkvmerge won't calculate a discard padding for this page. 2. For all other pages each packet's timestamp is calculated by adding each packet's number of samples to the previous Ogg page's end timestamp as given by its granule position. mkvmerge then calculates the discard padding for the last packet of the page by comparing the calculated end timestamp of that packet with the Ogg page's end timestamp as given by the granule position. As a workaround for certain rounding errors encountered in the wild, a discard padding of one sample will be treated as if no discard padding was present for all but the very last packet as indicated by the "end of stream" bit. Fixes #2280.
7 lines
387 B
Ruby
Executable File
7 lines
387 B
Ruby
Executable File
#!/usr/bin/ruby -w
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# T_645ogg_opus_first_timestamp_negative
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describe "mkvmerge / Ogg Opus with first granulepos being smaller than number of samples in packet = negative first timestamp"
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test_merge "data/opus/first-timestamp-negative.opus", :args => "--timestamp-scale 1000000"
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test_merge "data/opus/first-timestamp-negative.opus", :args => "--timestamp-scale 1000000 --disable-lacing"
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