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LibMedia: Convert FFmpeg time units to AK::Duration with integer math

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The existing conversion was rounding to the nearest millisecond, which
is much less precision than most videos will want. Instead, use only
integer math to directly convert the presentation time to seconds and
nanoseconds for our AK::Duration to represent accurately.
This commit is contained in:
Zaggy1024 2025-09-05 17:38:27 -05:00 • committed by Gregory Bertilson
commit cae14c763d
Notes: github-actions[bot] 2025-09-08 18:30:13 +00:00
2 changed files with 24 additions and 13 deletions
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35
Libraries/LibMedia/FFmpeg/FFmpegDemuxer.cpp
View file

@ -6,6 +6,7 @@
#include <AK/Math.h>
#include <AK/Stream.h>
#include <AK/Time.h>
#include <LibMedia/FFmpeg/FFmpegDemuxer.h>
#include <LibMedia/FFmpeg/FFmpegHelpers.h>
@ -51,15 +52,29 @@ ErrorOr<NonnullOwnPtr<FFmpegDemuxer>> FFmpegDemuxer::create(NonnullOwnPtr<Seekab
return demuxer;
}
DecoderErrorOr<AK::Duration> FFmpegDemuxer::duration_of_track_in_milliseconds(Track const& track)
static inline AK::Duration time_units_to_duration(i64 time_units, int numerator, int denominator)
{
VERIFY(numerator != 0);
VERIFY(denominator != 0);
auto seconds = time_units * numerator / denominator;
auto seconds_in_time_units = seconds * denominator / numerator;
auto remainder_in_time_units = time_units - seconds_in_time_units;
auto nanoseconds = ((remainder_in_time_units * 1'000'000'000 * numerator) + (denominator / 2)) / denominator;
return AK::Duration::from_seconds(seconds) + AK::Duration::from_nanoseconds(nanoseconds);
}
static inline AK::Duration time_units_to_duration(i64 time_units, AVRational const& time_base)
{
return time_units_to_duration(time_units, time_base.num, time_base.den);
}
DecoderErrorOr<AK::Duration> FFmpegDemuxer::duration_of_track(Track const& track)
{
VERIFY(track.identifier() < m_format_context->nb_streams);
auto* stream = m_format_context->streams[track.identifier()];
if (stream->duration >= 0) {
auto time_base = av_q2d(stream->time_base);
double duration_in_milliseconds = static_cast<double>(stream->duration) * time_base * 1000.0;
return AK::Duration::from_milliseconds(AK::round_to<int64_t>(duration_in_milliseconds));
return time_units_to_duration(stream->duration, stream->time_base);
}
// If the stream doesn't specify the duration, fallback to what the container says the duration is.
@ -67,8 +82,7 @@ DecoderErrorOr<AK::Duration> FFmpegDemuxer::duration_of_track_in_milliseconds(Tr
if (m_format_context->duration < 0)
return DecoderError::format(DecoderErrorCategory::Unknown, "Negative stream duration");
double duration_in_milliseconds = (static_cast<double>(m_format_context->duration) / AV_TIME_BASE) * 1000.0;
return AK::Duration::from_milliseconds(AK::round_to<int64_t>(duration_in_milliseconds));
return time_units_to_duration(m_format_context->duration, 1, AV_TIME_BASE);
}
DecoderErrorOr<Vector<Track>> FFmpegDemuxer::get_tracks_for_type(TrackType type)
@ -102,7 +116,7 @@ DecoderErrorOr<Vector<Track>> FFmpegDemuxer::get_tracks_for_type(TrackType type)
if (type == TrackType::Video) {
track.set_video_data({
.duration = TRY(duration_of_track_in_milliseconds(track)),
.duration = TRY(duration_of_track(track)),
.pixel_width = static_cast<u64>(stream->codecpar->width),
.pixel_height = static_cast<u64>(stream->codecpar->height),
});
@ -132,7 +146,7 @@ DecoderErrorOr<Optional<AK::Duration>> FFmpegDemuxer::seek_to_most_recent_keyfra
DecoderErrorOr<AK::Duration> FFmpegDemuxer::duration(Track track)
{
return duration_of_track_in_milliseconds(track);
return duration_of_track(track);
}
DecoderErrorOr<CodecID> FFmpegDemuxer::get_codec_id_for_track(Track track)
@ -181,15 +195,12 @@ DecoderErrorOr<Sample> FFmpegDemuxer::get_next_sample_for_track(Track track)
}
}();
auto time_base = av_q2d(stream->time_base);
double timestamp_in_milliseconds = static_cast<double>(m_packet->pts) * time_base * 1000.0;
// Copy the packet data so that we have a permanent reference to it whilst the Sample is alive, which allows us
// to wipe the packet afterwards.
auto packet_data = DECODER_TRY_ALLOC(ByteBuffer::copy(m_packet->data, m_packet->size));
auto sample = Sample(
AK::Duration::from_milliseconds(AK::round_to<int64_t>(timestamp_in_milliseconds)),
time_units_to_duration(m_packet->pts, stream->time_base),
move(packet_data),
VideoSampleData(CodingIndependentCodePoints(color_primaries, transfer_characteristics, matrix_coefficients, color_range)));

2
Libraries/LibMedia/FFmpeg/FFmpegDemuxer.h
View file

@ -38,7 +38,7 @@ public:
virtual DecoderErrorOr<Sample> get_next_sample_for_track(Track track) override;
private:
DecoderErrorOr<AK::Duration> duration_of_track_in_milliseconds(Track const& track);
DecoderErrorOr<AK::Duration> duration_of_track(Track const& track);
NonnullOwnPtr<SeekableStream> m_stream;
AVCodecContext* m_codec_context { nullptr };