Note that that it's also not correct for other codecs when the
sampling rate is greater than 65536. Right now it stores 0.
If in quicktime mode, it could use a SoundDescription v2 box, but in
mp4 that doesn't exist.
Per ISO 14496-12 , it should be using a AudioSampleEntryV1 along a
SamplingRateBox ('srat') which uses a 32 bits unsigned integer.
There's no handling of that in the current ffmpeg.
If time permit I will submit something for this.
Rgds
JY
On 25 August 2017 at 13:25, Jean-Yves Avenard <[email protected]> wrote:
> From 9baa7166fa96ed6beac9146c7e3b4dcf425a67d0 Mon Sep 17 00:00:00 2001
> From: Jean-Yves Avenard <[email protected]>
> Date: Fri, 25 Aug 2017 13:11:28 +0200
> Subject: [PATCH] Properly store sampling rate for FLAC in mp4
>
> Fixes ticket #6609
>
> Signed-off-by: Jean-Yves Avenard <[email protected]>
> ---
> libavformat/movenc.c | 28 +++++++++++++++++++++++++---
> 1 file changed, 25 insertions(+), 3 deletions(-)
>
> diff --git a/libavformat/movenc.c b/libavformat/movenc.c
> index 10b959ad02..aa4a9c962a 100644
> --- a/libavformat/movenc.c
> +++ b/libavformat/movenc.c
> @@ -1028,9 +1028,31 @@ static int mov_write_audio_tag(AVFormatContext
> *s, AVIOContext *pb, MOVMuxContex
> avio_wb16(pb, 0); /* packet size (= 0) */
> if (track->par->codec_id == AV_CODEC_ID_OPUS)
> avio_wb16(pb, 48000);
> - else
> - avio_wb16(pb, track->par->sample_rate <= UINT16_MAX ?
> - track->par->sample_rate : 0);
> + else {
> + uint32_t rate;
> + if (track->par->codec_id == AV_CODEC_ID_FLAC) {
> + /* When the bitstream's native sample rate is greater
> + than the maximum expressible value of 65535 Hz,
> + the samplerate field shall hold the greatest
> + expressible regular division of that rate. I.e.
> + the samplerate field shall hold 48000.0 for
> + native sample rates of 96 and 192 kHz. In the
> + case of unusual sample rates which do not have
> + an expressible regular division, the maximum value
> + of 65535.0 Hz should be used. */
> + rate = track->par->sample_rate;
> + while (rate > UINT16_MAX && (rate & 1) == 0) {
> + rate = rate >> 1;
> + }
> + if (rate > UINT16_MAX) {
> + rate = UINT16_MAX;
> + }
> + } else {
> + rate = track->par->sample_rate <= UINT16_MAX ?
> + track->par->sample_rate : 0;
> + }
> + avio_wb16(pb, rate);
> + }
> avio_wb16(pb, 0); /* Reserved */
> }
>
> --
> 2.11.0 (Apple Git-81)
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