On 24.02.2015 16:33, Tobias Rapp wrote:
Hi,
I am currently trying to interpret the index data of HuffYuv/PCM AVI
files written by FFmpeg. If the file is larger than 2GiB an "AVIX" RIFF
chunk is added for each 2GiB-block, each of these blocks gets an OpenDML
chunk index "ix00" and an OpenDML super index chunk "indx" is written
for each stream that contains the file offset of the according chunk
indexes together with its size and total duration.
For this super index "duration" entry the documentation I have found
states that it shall be the "time span in stream ticks" [1]. FFmpeg
seems to write the chunk count instead which is correct for video
streams where one data chunk "00dc" corresponds to one frame. For audio
streams one data chunk "01wb" usually contains multiple samples.
I guess for audio streams the "duration" should be multiplied by the
samples-per-chunk factor in avienc.c to allow third-party applications
to jump to the correct AVIX RIFF segment based on a given timestamp.
Any comments?
To illustrate my issue I have attached a patch that makes the OpenDML
super index chunk consistent with my interpretation of the specs. A test
with VirtualDub 1.10.4 shows that it also writes the audio duration
using sample count instead of packet count.
Using sample count allows to seek the audio stream to the right RIFF
segment without reading through all OpenDML standard "ix01" chunks.
Please comment,
Tobias
>From 3a8e15598fa3e044f3ef65b5063c633cb4b3afed Mon Sep 17 00:00:00 2001
From: Tobias Rapp <t.r...@noa-audio.com>
Date: Wed, 25 Feb 2015 17:10:13 +0100
Subject: [PATCH] libavformat/avienc: Fix duration for audio stream OpenDML
super index
Fixes the duration field of the OpenDML super index "indx" chunk to
contain the number of samples instead of the number of packets for
(linear/PCM) audio streams.
This matches the OpenDML V1.02 standard text which states that the
duration field shall contain "time span in stream ticks".
---
libavformat/avienc.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/libavformat/avienc.c b/libavformat/avienc.c
index 53c2fe7..b77b295 100644
--- a/libavformat/avienc.c
+++ b/libavformat/avienc.c
@@ -49,6 +49,7 @@ typedef struct AVIIentry {
typedef struct AVIIndex {
int64_t indx_start;
+ int64_t audio_strm_offset;
int entry;
int ents_allocated;
AVIIentry** cluster;
@@ -91,6 +92,7 @@ static int64_t avi_start_new_riff(AVFormatContext *s,
AVIOContext *pb,
avi->riff_id++;
for (i = 0; i < s->nb_streams; i++) {
AVIStream *avist = s->streams[i]->priv_data;
+ avist->indexes.audio_strm_offset = avist->audio_strm_length;
avist->indexes.entry = 0;
}
@@ -476,6 +478,7 @@ static int avi_write_ix(AVFormatContext *s)
for (i = 0; i < s->nb_streams; i++) {
AVIStream *avist = s->streams[i]->priv_data;
int64_t ix, pos;
+ int au_byterate, au_ssize, au_scale;
avi_stream2fourcc(tag, i, s->streams[i]->codec->codec_type);
ix_tag[3] = '0' + i;
@@ -511,7 +514,11 @@ static int avi_write_ix(AVFormatContext *s)
avio_skip(pb, 16 * avi->riff_id);
avio_wl64(pb, ix); /* qwOffset */
avio_wl32(pb, pos - ix); /* dwSize */
- avio_wl32(pb, avist->indexes.entry); /* dwDuration */
+ ff_parse_specific_params(s->streams[i], &au_byterate, &au_ssize,
&au_scale);
+ if (au_ssize == 0)
+ avio_wl32(pb, avist->indexes.entry); /* dwDuration (packet count)
*/
+ else
+ avio_wl32(pb, (avist->audio_strm_length -
avist->indexes.audio_strm_offset) / au_ssize); /* dwDuration (sample count) */
avio_seek(pb, pos, SEEK_SET);
}
--
1.9.1
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