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Put the MP4 index at the front of the file with +faststart #143

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Merged
zfleeman merged 1 commit into from
Nov 6, 2026
Merged

Put the MP4 index at the front of the file with +faststart #143

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4 changes: 4 additions & 0 deletions ffmpeg4discord/twopass.py
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Original file line number Diff line number Diff line change
Expand Up @@ -458,6 +458,10 @@ def _generate_params(self, settings: EncodeSettings, bitrate_targets: dict) -> d

params["pass2"].update(CODEC_OVERRIDES.get(codec, {}))

# MP4 only (same rule as `_output_filename()`): move the index to the front so a linked video starts playing sooner
if "vp9" not in codec:
params["pass2"]["movflags"] = "+faststart"

# Apply bitrate targets to both passes
for pass_params in params.values():
pass_params.update(**bitrate_targets)
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9 changes: 9 additions & 0 deletions tests/test_twopass.py
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Expand Up @@ -506,6 +506,15 @@ def test_x265_stats_path_escapes_ffmpeg_separators():
assert params["x265-params"] == r"pass=1:stats=C\:/Users/O\'Brien/Temp/ff4d-abc/x265_2pass.log"


@pytest.mark.parametrize("codec", CODEC_ENCODERS)
def test_run_puts_mp4_index_at_the_front(make_twopass, passes, codec):
make_twopass().run(make_settings(codec=codec))
*first, last = passes
has_faststart = "-movflags" in last.args and last.args[last.args.index("-movflags") + 1] == "+faststart"
assert has_faststart == (codec != "vp9") # vp9 writes .webm, which has no movflags
assert all("-movflags" not in p.args for p in first)


def test_hardware_codecs_have_no_stats_file(make_twopass, passes):
make_twopass().run(make_settings(codec="h264_nvenc"))
assert "-passlogfile" not in passes[0].args
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