You need to add "-loop_input" if the video input is a single frame,
and then you'll also need to add "-t " to make
ffmpeg finish the encoding because otherwise the looped image input
will run on past the end of the audio stream.
Also, if the audio is already mp3-encoded, it's probably better to use
"-acodec copy" to prevent degradation from re-encoding.
Actually, I'm not sure you need to upload h.264/mp3 to youtube; I'd
certainly try a format with ogg-encoded audio first.
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